Automotive Service Excellence A2 Course

Study Guide to become an ASE Certified Technician

ASE 2 - 1.1

TRANSMISSION THEORY AND OPERATION Understanding the operation of an automatic transmission is the first requirement for developing effective transmission/transaxle diagnostic and repair skills. Gear Principles One of the shortcomings of an internal combustion engine is that it doesn't develop enough power at low rpm to overcome the inertia of a vehicle. The speed range where it does produce enough power is impractical for maintaining either engine longevity or reasonable fuel economy. If you were to plot the torque output of an engine Throughout its rpm range, you would discover that torque increases as engine speed increased. However, this only occurs up to a point. After maximum torque is achieved (peak torque), will begin to fall off even as the engine rpm continues to climb, Since the engine can only develop one torque peak, it's the job of the transmission to manipulate that torque so that maximum power is available throughout the vehicle's driving range. The transmission accomplishes this torque multiplication by using various combinations of different sized input and output gears. The gear ratio refers to the number of revolutions that the input gear makes in relation To put the vehicle in motion requires maximum torque multiplication. This is the result when the drive gear is very small and the driven gear is very large. That means that the gear ratio is mathematically high. For example, if the drive gear turns three revolutions for every one revolution of the driven gear, the gear ratio is 3:1. In order to develop torque however, we must sacrifice operating speed. In other words, with a gear ratio of 3:1, output torque is greater than input torque, but output speed is less than input speed. This gear ratio is typical of first gear in a three-or four-speed transmission, when the crankshaft is turning three times as fast as the transmission output shaft. Some late model eight-, nine- and ten-speed transmissions have first gear ratios of 4:1 or more. Consequently, engine rpm remains high while the vehicle speed remains low. As the input and output gears be come closer in size, the operating speeds of each gear become more equal and the effect of torque multiplication is reduced. For example, the gear ratio in second will generally drop to 2:1. As the vehicle gains momentum, the gear ratio is further reduced to a direct drive or 1:1. This is typically the fourth gear ratio in a five- or six-speed trans mission and means that there is no torque multiplication at all. Most late model transmissions include one or two overdrive gears, like the fifth and sixth gears in a six-speed transmission. Overdrive occurs when the input or drive gear is larger than the output gear, resulting in a gear ratio that is less than 1:1. With this gear ratio, torque is actually reduced, but output speed is increased. This setup allows the engine to maintain a lower rpm at increased vehicle speeds, The Planetary Gear set Whereas manual transmissions use paired sets of gears chat rotate on parallel shafts to provide torque multiplication or reduction, most automatic transmissions use a planetary gear set. A basic planetary gear set consists of three primary components: the sun gear, the planetary pinion carrier, and the ring or internal gear. The sun gear is located in the center of the gear set, in the same way that the sun is positioned at the center of the solar system. This gear meshes with the teeth of the planetary pinion gears and can be either a spur or helical cut design. The planetary pinion gears revolve around the sum gear just like the planets orbit around the sun, Hence the name, planetary gear set. The planetary pinions are small gears that rotate within a cage called the planetary carrier this carrier, constructed of cast iron, aluminum, or steel, contains an individual shaft for each of the planetary pinion gears, and keeps these gears evenly spaced around the sun gear. Needle bearings are used between the planetary pinions and the carrier shafts. The planetary assemblies in most automatic transmissions use four, five, or six pinion gears, which are kept in constant mesh with both the sun gear and the ring gear. Surrounding the planetary carrier is the largest member of the gear set, known as the ring gear. The ring gear works like a band that keeps the entire gear set together. The ring gear is also called the internal gear or annulus, since its teeth are on the inside of the gear. These internal teeth mesh with and ride around on the planetary pinions. Most automatic transmissions rely on at least three planetary gear sets to transfer power and multiply engine torque to the drive axle. These are called compound gear sets, with the two most common designs being the Simpson gear set and the Ravingeaux gear set. In the Simpson gear set, two planetary gear sets share a common sun gear, while the Ravingeaux gear-set has a common ring gear with two sun gears and two sets of planetary pinion gears. Depending on the desired effect, the three components that comprise the planetary gear set (sun gear, ring gear and carrier) can be made to either revolve or remain stationary, Power flow typically occurs when one of the members is kept from turning, or if two of the members are locked together. Any one of the three parts of the planetary gear set can be used as the driving member or the driven member at any given moment. For example, while one part is turning, another part may be held stationary. Under this condition, the third member then becomes the output or driven member. Depending on which part is the driver, which part remains still, and which member is driven, the planetary gear set produces either an increase in torque or an increase in speed. In addition. the direction the output can also be reversed using various combinations. When a pair of externally-toothed gears are in mesh, the output rotates in the opposite direction of the input. However, when an externally-toothed gear is in mesh with an internally-toothed gear, both gears turn in the same direction These simple tips can help you remember the basics of simple planetary gear set operation: � If the planetary carrier is the drive or input member, the result overdrive. This means that output speed increases but output torque decreases � If the planetary carrier the driven or output member, the result is forward reduction or torque multiplication. This means that output speed decreases but output torque increases � With the sun gear driven clockwise and the planetary carrier held stationary, the ring gear will rotate counterclockwise producing reverse gear.

ASE 2 - 1.2

Planetary Gear Controls As we've discussed, certain components of the planetary gear set are typically kept from turning while others must be driven. It is the various combinations of these actions that provide the torque multiplication and output shaft rotational direction necessary for vehicle operation. Transmission clutches, bands and servos are devices used to accomplish these holding and driving asks, and are collectively referred to as the planetary gear controls. Clutches and bands are used in the automatic transmission to hold or turn members of the planetary gear sets. Clutches, whether multiple-disc or overrunning type, are devices capable of both holding and turning members of the planetary gear set. Bands on the other hand, are used solely to prevent members of the planetary gear set from rotating. The band is positioned around a drum that is attached to the planetary system. Band application is made possible through the action of the servo. The servo converts hydraulic pressure from the transmission fluid into a mechanical force. This causes the band to wrap tightly around the drum and prevent it from rotating. Since the band is larger than the drum it surrounds, the drum is free to rotate when servo apply force is reduced. The band is made from a section of spring steel with a layer of friction material mounted on the inside surface. Bands are rarely used in modern automatic transmissions today, but there are still some in use. The multiple-disc clutch assembly consists of a hub, friction discs, clutch plates, pressure plate, drum, piston and release springs. The purpose of this unit is to either apply holding action or transmit torque via the planetary gear sets. The friction discs, mounted on the hub, have internal teeth that are sized and shaped to mesh with the corresponding splines on the lurch assembly hub. In addition, these drive plates contain friction material that is bonded to both sides or just one side. The friction discs (drive plates) are alternately layered among the clutch plates. The clutch plates are flat steel discs with a smooth surface and outer serrations that engage with splines in the drum. The pressure plate is a single thick plate similar to the clutch places that is positioned at the top of the plate stack and held in place with a large snap ring. The pressure plate serves as a non-deflect-ing surface that provides the reaction to the engaging clutch pack, The dutch plates are free to float until the apply piston is actuated through hydraulic pressure acting upon it. Once this occurs, the piston forces the drive plates together against the pressure plate. Under this condition, the drum and hub are locked together and, consequently, rotate as a single unit. When the by hydraulic pressure is removed, the release springs force the piston back, which deactivates the clutch. Once the plates are separated, the drum disengages from the hub and the two turn independently of one another. ________________________________________________________________________________

ASE 2 - 1.3

One-Way Clutches A one-way clutch comes in a variety of configurations: 1. Roller clutch, 2. Sprag Clutch, 3. Racheting Clutch. As the name implies, a one-way clutch functions like a multiple-disc clutch, but only while rotating on one direction. When applied to the operation of a planetary gear set, the role of the one way clutch is broadened to a holder or driver. Both sprag and roller one way clutches can be applied to either a holding or driving application. For example, when the turbine shaft and inner race start to spin, the rollers are pushed down their ramps by the accordion apply springs. This action locks the inner and outer races together. Power is now transmitted from the inner race through the roller to the outer race. This connection drives the low reverse sun gear and direct clutch at turbine shaft sped. When the turbine shaft decelerates and starts spinning slower than the driven race, the one way clutch rollers reverse direction and begin to overrun (freewheel). This action unlocks the inner and outer races. As a result, the low reverse sun gear and direct clutch are disengaged from the turbine shaft.

ASE 2 - 1.4

Transmission Hydraulics Transmission fluid controls the action of the planetary gear sets by acting upon valves and pistons, and also transmits engine torque from the converter's impeller to the turbine. In addition, the fluid transfers heat from the transmission to the cooler assembly, which is typically located inside the radiator. The most well known principle common to the operation of all hydraulic systems is Pascal's Law. Blaise Pascal, a 17th Century French scientist, discovered two primary: characteristics about the behavior of liquids contained within a confined space, First, liquids cannot be compressed. Secondly, when pressure is applied to a liquid within a cased space, the pressure is exerted equally in all directions. Since liquids have no definite form of their own and can not be compressed, they will conform to the shape of the container in which they reside. This property allows transmission fluid to be used in a variety of ways to accomplish work throughout the transmission. To illustrate Pascal's second discovery concerning the pressure of liquids within a closed space, let's fill a one sq. in. cylinder with fluid and apply a force of one pound to the top of the liquid's surface. According to Pascal's Law, we have not only exerted a force of one pound per sq. in. (1 psi) on the liquid's surface, but to all areas of the container as well. A distinct relationship exists between force and piston area within a sealed hydraulic system. If we take that one pound per sq. in. of force and apply it to a 3 sq. in. piston, the piston will generate a pressure of 3 psi even though the initial force is only one psi. This is how a hydraulic system is able co multiply force. The formula you need to know in order to calculate force multiplication can be expressed in three ways: � Force � Pressure = Area � Force � Area = Pressure � Pressure x Area = Force ________________________________________________________________________________

ASE 2 - 1.5

Transmission Pump The transmission oil pump is typically driven at engine speed by the torque converter shell. It's used to circulate fluid throughout the transmission as well as develop hydraulic pressure. Most automatic transmissions use either a fixed-displacement (gear-type) pump, or a variable-displacement (vane-type) pump. The fixed displacement pump always moves the same amount of oil regardless of the transmission's needs. In contrast, the variable displacement pump adjusts the volume of oil output according to the transmission's needs through the use of a slider valve. The slider is placed around the root and vanes and is held against the pump body by a priming spring. In this position, maximum pump output is achieved. However, when the pressure regulator valve exhausts oil pressure to the pump, the fluid pushes on the slider valve compressing the priming spring. This lowers pump output.The concept of how pumps move liquids is often misunderstood. While many technicians believe a pump draws a liquid in, what actually takes place is quite different. Liquids are transferred in a pump from an area of high pressure (atmospheric pressure) to an area of low pressure (below atmospheric pressure). As the pump turns, an area of low pressure is generated at its inlet chamber. The transmission oil pan or sump is kept at atmospheric pressure through a vent in the transmission case, Since the pressure acting on the fluid in the sump is greater than the pressure at the pump's inlet, fluid is forced into the pump. From there, fluid is picked up by the pump gears, which direct it toward the pump's outlet chamber where it is squeezed out of the pump.

ASE 2 - 1.6

ASE 2 - 1.7

Pressure Regulator Valve Without pressure regulation, fluid pressure in the pump would increase until the pump stalled. The pressure regulator valve is intended to prevent this condition by maintaining a stable operating pressure throughout the speed range of the engine. The position of the pressure regulator valve can be affected by a computer controlled solenoid which is typically called the pressure control solenoid. As the pump rotates, output pressure is routed to the pressure regulator valve, which is held closed by a spring. Once pump (line) pressure rises above the spring calibration point, the regulator valve opens and uncovers an exhaust port. With the exhaust port uncovered by the regulator spool valve, fluid pressure in excess of transmission demands is routed back to the pump on variable displacement units, or to the transmission sump on those applications that use a fixed displacement pump. The action of the pressure regulating valve typically maintains a high pressure to keep the multi-plate clutches from slipping should solenoid power be lost. The high pressure can be decreased by a pressure control solenoid based upon engine load, throttle position, and other sensor inputs. The primary responsibilities of pressure regulation include: charging the torque converter, exhausting fluid pressure, and maintaining a balanced condition.

ASE 2 - 1.8

Accumulator Another device used to affect shift feel based on engine load is the accumulator. An accumulator contains a spring-operated piston that temporarily absorbs hydraulic pressure in a band or clutch apply circuit, For example, since the engine only develops a small amount of torque at light throttle pressure, the clutch requires less apply force to hold a dutch housing. However, under heavy throttle conditions, when the engine produces a larger amount of torque, more apply pressure is needed to hold the clutch housing. If the clutch applies too quickly, the shift will be hard. If the clutch applies too slowly, it will slip and burn, due to the heat generated by the excessive friction. In this case, the accumulator regulates dutch apply pressure to cushion clutch application based on throttle opening.

ASE 2 - 1.9

Torque Converters The torque converter is fluid coupling device used to transfer engine torque from the crankshaft to the transmission. A simple example of the fluid coupling operational principle can be demonstrated using pair of fans positioned face-to-face. With only one fan turned on, the other fan will spin even though no mechanical link exists between the two. The operating fan represents the converter's impeller, the air between the two fans represents automatic transmission fluid, and the unplugged fan represents the converter's turbine. The fluid coupling that occurs inside the torque converter is what gives the automatic transmission the ability to be truly automatic. Since the impeller doesn't move much fluid at low engine speed, the engine can run easily at idle while the vehicle remains motionless. This can be seen in the operation of the two opposing fans. When the blade of the unplugged fan is held still, the other fan will continue to run. It is this feature of the torque converter that eliminates the need for mechanical disengagement of the engine and transmission when the vehicle is idling in gear. A conventional torque converter is composed of four primary components: the impeller or pump, the stator, the turbine, and the converter clutch. The impeller is the drive (input) member, and is mechanically linked to the engine's crankshaft via the flex plate. The turbine is the driven (output) member. It is splined to the turbine shaft, which connects to the forward clutch assembly in the transmission. The stator is the reaction member, and fits in between the impeller and turbine. The converter clutch is splined to the turbine can be connected to the converter housing cover to establish a direct connection between the sengine crankshaft and the transmission input shaft. The weight of the torque converter is supported on the engine side by a short protrusion emanating from the front half, which fits into a pocket at the rear of the engine's crankshaft. At the rear of the converter is a hollow shaft containing two notches or flat spots. These notches or flat spots, positioned 180 degrees apart, are used to drive the transmission oil pump. The rear of the converter is supported by a bushing or bearing at the front of the transmission located within the pump housing. The impeller, which forms the rear half of the converter shell, contains numerous curved blades that rotate as a single unit. Because it is driven directly by the crankshaft, the impeller turns at engine speed. Consequently, it acts like a pump to start the transmission fluid circulating inside the torque converter. Looking inside the converter shell, the blades of the impeller face the rear of the engine, while the turbine blades face the front of the transmission. Therefore, the impeller and turbine blades are positioned face-to-face with one another. The turbine uses blades similar to the impeller, however, the turbine blades have a greater curve to them. This promotes greater fluid coupling efficiency. After the engineers reach the design limits of the fluid coupling (impeller and turbine), a stator is added. The stator is positioned between the impeller and turbine, and has no mechanical connection to either of the two. It contains specifically angled blades around both sides of its circumference to redirect the flow of fluid coming off the turbine. This action increases the force of the fluid driving the turbine, resulting in torque multiplication. Because of this, it is the stator that changes the fluid coupling (impeller/turbine) into a torque converter. The stator is supported by an overrunning roller clutch that permits it to turn freely in one direction, and lock up in the other. The medium used to transfer energy in the torque converter is automatic transmission fluid. Fluid flows inside the converter in two different Ways. When the fluid flows around the circumference of the torque converter due to the rotation of the converter on its axis, it is known as rotary fluid flow. The flow of fluid that occurs between the impeller and turbine is referred to as vortex oil flow. As vortex flow increases, turbine speed approaches impeller speed. This is called the coupling point. However, because of the inherent slippage that occurs in a fluid coupling, the impeller and turbine cannot rotate at the same speed As the engine drives the impeller, centrifugal force propels the oil outward. The faster the impeller spins, the greater the increase in centrifugal force. As the oil is thrown outward from the impeller, it strikes the curved blades of the turbine, causing it to turn in the direction of engine rotation. However, since engine speed is low during idle, the impeller turns slowly and little centrifugal force is generated inside the torque converter. This is why the vehicle can be held still when engine rpm is low and the brakes are applied. Under this condition, lite or no power is transferred to the transmission. As mentioned earlier, the stator redirects the flow of fluid as it is thrown off the turbine blades. As engine speed rises above idle. Fluid from the turbine hits the front side of the stator blades. Since the action of the roller dutch keeps the stator locked in that direction, the stator deflects the fluid back on the turbine, thus preventing the fluid from impeding impeller rotation. With more impeller energy available to act on the turbine, the engine torque delivered to the turbine is multiplied and the vehicle starts to move. Because of the difference between the impeller and turbine speeds as the vehicle begins to travel forward, the stator remains in a stationary (locked) position. This occurs when the inner race rotates counter clockwise. In this direction, the accordion springs force the rollers down the ramps of the cam pocket, wedging the inner and outer races together. As the vehicle gains speed, the centrifugal force inside the converter changes the direction of fluid coming off the turbine blades. This change of direction occurs when the converter reaches its coupling speed. The fluid from the turbine now hits the back side of the stator blades, causing the roller dutch to overrun. The action of the one-way cutch now allows the stator to spin freely. Under this condition, fluid is no longer redirected and engine torque delivered to the turbine ceases to be multiplied. ________________________________________________________________________________

ASE 2 - 1.10

Torque Converter Clutch Even while operating at peak efficiency, a torque converter experiences up to a 10% energy loss (slip) when it reaches the coupling point. This wasted energy is dissipated in the form of heat created by the slippage between the impeller and the turbine. It is this heat source that poses the greatest threat to the life of the transmission fluid. The Torque Converter Clutch (TCC) is a device that captures this otherwise lost energy. By doing so, the TCC increases fuel economy, prolongs the life of the transmission fluid and also extends engine life by keeping rpm lower at higher vehicle speeds, The converter clutch operates in the same way as the manual transmission clutch in that it mechanically links the engine and transmission together. The conventional torque converter makes it possible to operate at near 100 percent efficiency, There are at least two types of converter clutches. One design, the TCC, allows for a complete lockup of the torque converter with zero rpm slip speed between the Engine crankshaft and the transmission input shaft. Another design, the Variable Capacity Converter Clutch (VCCC) allows for a partial lockup of the torque converter with a predetermined small amount of allowed slip speed between the engine crank shaft and the transmission input shaft This small amount of slip is typically in the 35 rom range, The lockup clutch design uses a pressure plate, damper, and a clutch friction ring as its principal members. The complete assembly is located between the front of the turbine and the interior front face of the converter shell. The damper assembly contains several coil springs that are used to absorb the shock of clutch engagement. The front portion of the turbine shaft is drilled lengthwise to form a passage for fluid flow. This allows fluid to be applied and exhausted from a chamber between the front side of the pressure plate and the torque converter shell, The lockup clutch is activated by a solenoid under computer control. This type of clutch regulation is much more precise since it is based on a variety of engine variables as well as vehicle speed. When the vehicle reaches converter clutch engagement speed, and the other conditions such as throttle position, manifold pressure, and engine temperature are right, the computer will activate the solenoid. This allows line pressure fluid to enter the converter apply passage, where it flows through the turbine shaft to the apply side of the converter clutch. ________________________________________________________________________________

ASE 2 - 1.11

Electronic Transmission Control Electronically controlled transmissions are shifted based on a variety of sensor input data. The Throttle Position (TP) sensor and the Ve hide Speed Sensor (VSS) signal are the two primary data inputs that are used to control overall transmission operation. Manifold Absolute Pressure (MAP) sensor, Mass Air Flow (MAF) Transmission Fluid Temperature (FT) sensor. Transmission Range (TR) sensor, Transmission Input Speed sensor ISS) and Trans mission Output Speed sensor (OSS), and others are used to fine rune the shift timing, shift speeds, shift quality, and torque converter clutch operation. Sensor data is sent to the Powertrain Control Module (PCM) or Transmission Control Module (TCM), which in turn controls the shift solenoids, pressure control solenoids and torque converter clutch solenoids Some of the advantages of electronically-controlled transmissions include: � Improved fuel economy � On-board diagnostic capability � Calibration flexibility � Adaptive learning � Reduced valve body complexity. The onboard diagnostic capability of electronic transmissions allows a technician to pinpoint problem areas. Another bonus to electronic control is the ability to change shift points simply by recalibrating the control module. In addition, adaptive learning is a function that allows the control module to conform transmission shifting based on driver habits. Let's take a brief look at the operation of an electronic transmission. Solenoids are used to control the flow of hydraulic fluid for shift pattern (upshifts and downshifts), shift quality (how each shift feels), and torque converter clutch operation. Depending on the application, these solenoids may either permit or block fluid flow when energized. The computer continually processes incoming sensor signals to determine when a solenoid should be activated or deactivated, There are two types of solenoids and two stares of default operation for each solenoid: 1. On/Off solenoids. These solenoids are either on or off. In one state, they will allow pressurized fluid to pass through them. In the ocher state, they will block fluid from passing through them. The default operational state (power off) of these solenoids can be normally closed (blocking fluid passage) or normally open (allowing fluid through a passage). 2. Pulse-Width Modulated (PWM) solenoids. These solenoids are used to vary fluid the pressure in a hydraulic circuit, they can make the fluid pressure or volume increase or decrease in gradual increments. The default operational state (power off) of these solenoids can be normally closed (blocking fluid passage) or normally open (allowing fluid through a passage). The positions of these solenoids determine the correct upshift and downshift points for all driving conditions. By balancing this pair of solenoids, the computer can command the various shift valves when to up shift or downshift based on the speed of the vehicle and throttle position sensor inputs.

ASE 2 - 2.0

Mechanical/Hydraulic Systems.txt The most vital step in making a correct diagnosis is listening carefully to the customer's complaint. Asking the right questions can save time in pinpointing a transmission malfunction. How is the vehicle performing differently and what symptoms have they experienced? Did the problem become noticeable gradually or suddenly and when did it first start? Have they heard any strange noises or smelled any unusual odors? Have they noticed any puddles or stains on the ground under where the vehicle was parked? Discuss with the customer the difference between normal and abnormal transmission operation, to eliminate chasing a problem that may not exist at all or may not be transmission related. If the vehicle is new to the customer, it may be performing properly, albeit differently than their previous vehicle. Of course, you will need to road test the vehicle to verify the customer's complaint, but before the road test, a preliminary inspection should be performed.

ASE 2 - 2.1

Preliminary Inspection Before road testing the vehicle, perform a visual inspection of the transmission and the rest of the vehicle. Check the transmission fluid level and condition and check for fluid leaks. Check the manual shift and throttle valve linkage adjustments. Inspect the condition of the vacuum hoses and electrical wiring and their connections to the transmission. Check for non-original size tires and other modifications that could affect transmission operation Check for Technical Service Bulletins (TSBs) that may reveal a factory recall, service campaign or updated repair information regarding the symptoms or system in question. Doing research at this point could save valuable time that would otherwise be needlessly spent trying to achieve a diagnosis. Make sure the engine is in good running order. This is important because sometimes symptoms that are caused by a poor running engine can be mistakenly attributed to the transmission. For example, a lean running engine will have low manifold vacuum, which would cause a vacuum modulator or the electronic control system to indicate engine load that does not actually exist, in turn causing harsh and delayed shifts. Always make sure the engine is operating properly and if needed, perform all necessary repairs before proceeding with transmission diagnosis. If a Malfunction Indicator Light (MIL) remains illuminated after the engine is started, check the computer for stored Diagnostic Trouble Codes (DTCs). Finally, be sure to check the condition of the powertrain mounts. One of the most overlooked causes of transmission problems is broken powertrain mounts. A broken mount can allow excessive movement of the powertrain, which can cause the shift linkage to bind and can also cause noise and vibration.

ASE 2 - 2.2

Transmission Fluid Level Always follow the manufacturer's recommended procedure for checking fluid level. As a general rule, park the vehicle on level ground and apply the parking brake. Traditionally most transmissions used a dipstick to indicate fluid level, but many newer transmissions have a fluid level control plug, Most manufacturers specify that the engine be running when the fluid level is checked, but on some vehicles the engine must be turned off. Usually fluid level is checked with the transmission at normal operating temperature, however many manufacturers indicate that the fluid should be within a specific temperature range, so always refer to the vehicle service manual. It is important to observe these specified fluid temperatures because many transmissions have a thermostatic element that restricts fluid flow at certain temperatures. These elements contain temperature sensitive strips of metal that react to fluid temperature changes and open or close a fluid passage. Checking the fluid level at the wrong temperature could produce an incorrect reading. There are several ways to determine the actual temperature of the fluid. A flexible temperature probe and a digital voltmeter can be used. The probe is a transducer that converts the actual fluid temperature into an electrical signal, and the meter then displays the number in degrees Fahrenheit or Centigrade depending upon your selection. On many electronic transmissions there's an oil temperature sensor that reports to the computer. Fluid temperature on these transmissions can be displayed on a scan tool by accessing the control module's data stream. The following is a typical procedure for checking fluid level with a dipstick: Start the engine and allow it to reach the specified operating temperature. Next, move the gear selector through each range slowly, then place the gear selector in Park or Neutral, as required. Clean any dirt from the dipstick and tube, then remove the dipstick and wipe it clean. Insert the dipstick back into the tube until it is fully seated, then pull the dipstick from the tube and read the fluid level. If the fluid level is low, add the type of fluid specified by the vehicle manufacturer, but only enough to bring the fluid to the proper level. An overfilled transmission is as bad as an under filled one. When the unit contains too much oil, the fluid will start to foam. This causes the transmission oil to become aerated, diminishing its apply-pressure capabilities. Remember, fluid is nor compressible, but air is, and aerated fluid contains many tiny air bubbles. Also, an overfilled transmission can create a fire hazard if the fluid backs up through the fill tube and splashes onto a hot engine. On the other hand, too little fluid will create poor shifting, which can lead to an overheated transmission. The following is a typical procedure for checking fluid level with a control plug: Start the engine and allow it to reach the specified operating temperature. Next, move the gear selector through each range slowly, then place the gear selector in Park or Neutral, as required. Remove the fluid vent cap and fluid level control plug. The fluid level should be even with the bottom of the threaded plug hole. If the fluid level is low, add the fluid specified by the vehicle manufacturer until fluid drains from the plug hole. Once the fluid stops draining, reinstall the control plug and tighten to spec. ________________________________________________________________________________

ASE 2 - 2.3

Transmission Fluid Condition While checking the fluid level, inspect the condition of the fluid. Transmission fluid is dved red in order to distinguish it from engine oil and other fluids, but as the fluid ages, its color darkens. This color change resulrs from normal use and is not a sign of fluid breakdown. Very dark brown or black fluid, however, is a sign of dirt or burned friction material. Fluid that smells burned usually indicates the transmission is slipping or overheating, If you find varnish on the dipstick accompanied by a varnish like odor, that's a sign of transmission fluid breakdown. The varnish is a by-product of the oxidized fluid and is typically the result of severe use like trailer towing and/or fluid change neglect. Metallic particles found in the Aid indicate transmission wear and the fluid pan should be removed for further investigation. The presence of iron filings is a sign of gear and/or clutch drum damage, and gold partides 2would be from bushing and/or thrust washer wear. If the fluid is pink with a milky consistency, then the transmission cooler in the radiator has ruptured contaminating the fluid with coolant. Repairing the radiator and changing the fluid will not rectify the condition, however, since the combination of engine coolant and transmission fluid destroys clutch friction material and transmission seals. The only remedy here is a complete transmission overhaul and torque converter replacement.

ASE 2 - 2.4

Transmission Fluid Leaks Locating the source of a transmission fluid leak can be an involved process since there are so many potential leak areas. The first step is to make sure that it's actually transmission fluid that's leaking, and not engine oil or power steering fluid. Remember, leaks in these arcas will eventually work their way onto the transmission pan as a result of the air Howing underneath the vehicle. In addition to a leaking pan gasket, side cover gasket and axle seals (transaxle), other potential transmission leak areas include: speed sensors, electrical connector seals, cooler line fittings, fill pipe seal, porous transmission case, line pressure and fluid level check plugs, torque converter (weld leaks), and output shaft seal. Operate the vehicle until the transmission fluid reaches normal operating temperature. Raise and safelyvsupport the vehicle and inspect the transmission for leaks. If you can't pinpoint the source of the leak, use a sate, suitable solvent to can the transmission or steam clean it to remove any grease or road dirt, and repeat the visual inspection procedure. If the exact source of the leak still cannot be pinpointed, try using an aerosol talcum powder. When using a powder test, clean the area thoroughly and spray the suspected area with a light coat of powder. This fine layer of powder will provide a perfect surface for capturing the flow pattern of the leak. Run the vehicle and perform a visual inspection. At this point, the leak should be traceable across the powder. Another leak detection method is using a black light. This procedure involves pouring an ounce of fluorescent dye into the transmission. Opcrate the vehicle to allow che dye to mix with the transmission fluid, then perform a visual inspection. As the dye oozes out along with the fluid, it will appear bright yellow at the leak source under the black light.

ASE 2 - 2.5

Manual Shift Linkage If the manual shift linkage is not properly adjusted, it may result in any of the following sympcoms in cluding: a no-start in park or neutral vehicle creep in neutral, premature clutch or band wear, and improper shift timing. When the gear sclector is moved, the manual shift linkage must exactly position the valve in its bore. If the linkage is damaged or improperly adjusted, hydraulic circuits may be opened to line pressure when they should be closed Once in these circuits, the main control pressure may affect valve movement, which can affect shift timing. To check the manual shift linkage adjustment, apply the parking brake and move the gear selector through each range with the engine off. Feel for the detents inside the transmission as you move the gear selectot, and make sure the pointer or lever aligns with the proper gear position When the gear selector is placed in Park. the parking pawl should engage. Finally, make sure the starter engages only when the gear selector is in Park or Neutral. ________________________________________________________________________________

ASE 2 - 2.6

Road Testing After the preliminary inspection, thorough road test should be performed to verify the customer's complaint. Perform the road test on a familiar route that includes a variery of driving conditions. During the road rest, check the shift timing and quality and check the torque converter and torque converter clutch operaton. Check for evidence of slippage and listen and feel for unusual noises and vibration. Depending on the problem, connect a hydraulic pressure gauge, to monitor hydraulic pressure, and a scan tool to check solenoid status and commands.Check the shift timing and shift qualiry at various throttle opening positions. Refer to the manufacturer's shift speed specifications to compare to the acrual vehicle's performance. Note that these specificatons are affected by non-original tires sizes and final drive ratios. A durch and band application chart should be used to determine what planetary gear control devices are engaged in each gear position. ________________________________________________________________________________

ASE 2 - 2.7

Pressure Testing By connecting a pressure gauge to specific access points located on the transmission case, the fluid pressure can be observed to see if it's at the proper level based on range selection and rpm. Recording line pressures enables you to spot potential problems in the oil pump, pressure regulator valve, and pressure control solenoids, etc. To pressure rest a transmission, pressure gauges that register up to 300 psi will be needed and a scan tool, since the tests will be performed at specific engine speeds, Raise and safely support the vehicle, then connect the gauge(s) co the pressure points). Operate the vehicle to bring the transmission to normal operating temperature. Make sure the transmission fluid is at the proper level. Follow the service information instructions for checking the fluid pressure with the scan tool. Many scan tools can command the pressure control solenoid to cause fluid pressure changes. The pressure gauge should respond to the commanded fluid pressure changes for each gear range. Compare the recorded pressure readings with manufacturer's specifictions. If the fluid pressures do not match the specified fluid pressures for each range, follow the diagnostic table in the service information to diagnose the problem. When evaluating pressure test results, you will need to know how the fluid flows through the transmission hydraulic circuits. Vehicle manufacturers supply diagrams that show Auid flow in each gear range. ________________________________________________________________________________

ASE 2 - 2.8

Air Pressure Tests Locating the source of a hydraulic problem can often be difficult. If your diagnosis has uncovered a slipping band or clutch, an air pressure test can be performed to isolate the problem to either the apply device or the valve body. Once the valve body has been removed, air pressure can now be introduced into transmission case passages leading to the lurches or servos. A blowgun with a rubber nozzle is used for this purpose. To simplify the process of identifying these and other hydraulic circuits in the transmission, specific adapter plates are available. The adapter plate bolts to the transmission (valve body removed) and seals the case apply passages, WARNING: To prevent injury, Eye protection must be worn when performing air pressure tests. Apply approx. 40-psi pressure to the marked test holes in the plate. When air is applied to a clutch test port, a dull thud should be heard or movement of the piston felt when the clutch piston is applied. If the clutch seals are leaking, a hissing sound will be heard. Observe the bands and make sure they tighten when air pressure is applied to the servo test ports. The servos should hold air pressure without leaking The bands should loosen when air pressure is released and a dull thud may be heard when the servo piston returns to the released position. When air is applied to the governor test port, a sharp clicking or whistling noise will be heard if the governor is moving properly. ________________________________________________________________________________

ASE 2 - 2.9

Stall Speed Testing The stall test measures the peak rpm of the engine in gear while the brakes are applied. Engine speed under this condition is limited by the angle of the blades in both the impeller and turbine. The greater the blade angle is, the lower the stall speed will be, since the resistance to fluid flow is higher. The purpose of the stall speed rest is to verify the operating condition of the torque converter and the condition of the various planetary gear control devices. In addition, this rest can also spot engine performance problems. To conduct this test, connect a tachometer (unless there is already one on the instrument panel) to the engine and position it inside the vehicle. The transmission fluid should be at normal operating temperature before performing this test. Apply the parking brake and place blocks in front of and behind the drive wheels. With the engine running and the transmission in gear, keep the brakes fully applied throughout the test. Now press the accelerator to the floor and hold it there just long enough (no longer than 5 seconds) to allow the engine to reach full rpm. Quickly note the rpm and release the throttle. The stall rest is generally performed in low, reverse, drive, and overdrive (if applicable) Place the transmission in Neutral and run the engine at fast idle for 30-60 seconds, in between each rest, to cool the torque converter. If the stall speed is higher than factory specifications in a particular gear range, one or more of the planetary gear control devices is slipping. Refer to the clutch and band application chart for the transmission in question to see what devices are applied in this gear. If the stall speed is below specifications, it would indicate that either an engine performance problem was present, or that a stator clutch had failed. For example, if the exhaust system was restricted, the engine would be unable to rev and the result would be a lower than normal stall speed. If engine performance is OK, and the stall speed is too low, then the problem would be a freewheeling stator clutch. Since the stator clutch locks below converter coupling speed, it allows the stator to deflect the oil back to the turbine. If the stator clutch freewheels in both directions, the turbine oil will now be thrown back at the impeller, hindering its rotation. This condition will prevent the engine from reaching a normal stall speed. ________________________________________________________________________________

ASE 2 - 2.10

Common Noise Complaints Diagnosing a transmission noise or vibration problem is not always simple. Keep in mind that noises detected during a road test may actally have nothing to do with the transmission. The following symptoms are common transmission-related noise and vibration complaints. Buzzing Buzzing noises are usually the result of a pressure regulating valve or sealing ring malfunction. Such noises will fade in and out in relation to engine speed. Constant Rattling Rating that usually reveals itself at low speeds may be due to something as simple as loose torque converter attaching bolts, or something more serious like broken impeller or turbine vanes. Gear Noise Gear noise in the first gear range usually indicates a bad planetary gear set. Once a higher gear is attained, the gear noise may go away if the gear set is defective. If the noise persists to the next shift, you should suspect defective bushings or thrust bearings. Gear noises may be less perceptible or even disappear after an upshift. Intermittent Rattling Intermittent rattling that occurs at low speeds or when the vehicle is idling in gear, points to a cracked flex plate. Pump Noise Pump noise is characterized as a high-pitched whine that increases with engine speed. This problem is present in all gear ranges and occurs at idle when the transmission is in gear. Ratcheting Noise Check for a weak parking pawl return spring Squeal A squeal that occurs at low speeds is typically the result of a faulty speedometer driven gear. Vibration Vibration from filler or cooler lines is a common problem that occurs due to broken or loose line brackets. While tightening loose bolts or replacing a broken bracket is an easy fix, consider that the condition may have occurred due to faulty engine/transmission mounts, which allowed excessive powertrain movement. Whining A steady whine at idle that may or may not become worse as engine speed is increased, could indicate a low oil level. If the noise is more noticeable in first or reverse gear and is related to vehicle speed, suspect a gear problem. During stall tests, a whining noise is considered normal due to the fluid flow through the converter. Other Possibilities If the noise or vibration is most noticeable with the vehicle idling in park or neutral, but diminishes as engine rpm increases, check for poor engine performance or some other non-transmission related area as the potential source of the problem. Here are some additional items to check: � Tires for uneven wear, imbalance and mixed or improper tire sizes. � Suspension components and fasteners for looseness and rubber components for deterioration, � Engine/ transmission mounts for looseness and/or possible deterioration. � Transmission case mounting holes for cracks, missing bolts, nuts and studs. Also, inspect the bolts for stripped threads. � Flexplate for imbalance, cracks and loose or missing bolts. ________________________________________________________________________________

ASE 2 - 3.0 ELECTRONIC SYSTEMS

Depending on the vehicle, transmission control is either integrated into the engine computer or PCM (Powertrain Control Module), or relies on a separate transmission computer or Transmission Control Module (TCM). In either case, the computer receives inputs from sensors and in turn uses the information to determine shift timing and feel and TCC application. Some inputs come from engine related sensors such as the Mass Air Flow (MAF) sensor and Engine Coolant Temperature (ECT) sensor, which inform the computer of the load and temperature under which the engine is operating. Other inputs come from sensors on the transmission itself, such as the Vehicle Speed Sensor (VSS), Transmission Range (TR) sensor and the Transmission Fluid Temperature (TFT) sensor. Still other inputs come from the driver in the form of accelerator pedal position, which is communicated to the computer by the 'Throttle Position (TP) sensor. The PCM or TCM uses certain solenoids to accomplish shift and TCC control. Among these are solenoids for shifting, a solenoid for TCC control and may also include an electronic pressure control solenoid for controlling transmission line pressure and timing/coast clutch solenoids to control downshift timing and feel. ________________________________________________________________________________

ASE 2 - 3.1

Preliminary Inspection When an electronically-controlled transmission develops problems, follow the same basic diagnostic approach that you would use for a conventional unit. Check for TSBs, make sure engine performance is satisfactory, check transmission fluid level and condition, and check for leaks. Carefully inspect the wiring, connectors and components of the transmission control system. This includes not only those on the transmission bur also the engine sensors that affect transmission control. Depending on the circuits involved, faulty wiring and poor connections can cause a variety of shifting problems. Inspect the wiring for cuts and abrasion and contamination from oil or transmission fluid. Disconnect the electrical connectors and inspect the terminals for corrosion, distortion and contamination. Connectors that are in poor condition should be replaced. Wiring can be repaired in some cases using a quality splice (soldering joints and using heat shrink tubing), however, many manufacturers recommend that damaged wiring in computer circuits only be replaced with a new harness. Many transmission malfunctions will set a Diagnostic Trouble Code (DTC) in the computer, and in some cases illuminate a Malfunction Indicator Light (MIL) on the dash. Once all of the basic checks have been made, check the computer for stored D'TCs, even if the MIL is not illuminated. Each system will come with a specific number of DTCs that are assigned to various circuits and components. ________________________________________________________________________________

ASE 2 - 3.2

Diagnostic Trouble Codes When vehicle manufacturers began using electronics and onboard computers to control engine and transmission functions, onboard diagnostics were developed as a part of these systems to aid in the diagnosis of vehicle problems. With on-board diagnostics, the PCM or TCM monitors the input and output circuits in the system and compares their voltage, resistance or current values with preprogrammed parameters. If an abnormal signal is detected, a fault is stored in the computer's memory in the form of a DTC. There are two kinds of DTCs. A hard code represents a current problem in the system, while a soft code is an intermittent problem or a malfunction that occurred in the past, but is not present at the time of DC retrieval. Intermittent codes are usually stored for a specific number of key ON/OFF cycles, and are then erased from the computer's memory if they do not reappear during that period. Hard codes should be addressed first during diagnostics. On pre-OBD II vehicles, DTCs stored in the computer's memory can be retrieved in several ways. On some vehicles, a jumper wire can be connected between terminals of the DLC (Data Link Connector), which causes the control system to go into self-diagnostic mode. The MIL then flashes and codes can be read by interpreting the flashes with a service manual. On other vehicles, the codes can be read on a digital display on the instrument panel. A scan tool can also be used to obtain DTCs on pre-OBD Il systems, but the number of components monitored by the control systems on these vehicles varied from manufacturer to manufacturer and each manufacturer had their own nomenclature and code numbers. A scan tool must be used to obtain codes from OBD II vehicles. OBD I requires on-board diagnostic systems to detect problems before they can result in increased emissions. In OD I systems, components are monitored for deteriorating performance rather than just total failure. Prior to OBD I, vehicle manufacturers used two and three digit codes that were proprietary to specific vehicles and systems and each manufacturer also had their own code definitions. With OBD I, common codes and definitions were developed to identify all basic emissions-related failures. OBD I trouble codes consist of one alpha character followed by four digits. The alpha character indicates the area of the vehicle where the failure occurred. This includes (B) Body, (C) Chassis, (P) Powertrain, and (U) Network. The first digit of the DTC denotes the origin of the code. Codes authored by the Society of Automotive Engineers (SAE) are identified by a zero (0). These codes are known as generic DICs since they are the same for every vehicle. Manufacturer specific codes are indicated by the number one (1). These DTCs are part of the manufacturer's enhanced diagnostic software, and vary between brands. The second digit in the DTC identifies the system experiencing the problem, while the last two digits correspond to a specific code definition. ________________________________________________________________________________

ASE 2 - 3.3

Scan Tools Before using a scan tool, read the manufacturers instructions to become familiar with its operation. Most scan tools are equipped with removable cartridges that contain specific vehicle service information. The proper cartridge must be installed for the vehicle being serviced. To stay up to date, new cartridges must be purchased as required, although some cartridges can be updated by downloading information from a computer. Make sure the ignition key is in the OFF position, then connect the scan tool connector to the DLC. On pre-OBD II vehicles, the location of the DLC varied according to manufacturer. On all OBD Il vehicles, the DLC is located under the dash on the driver's side of the vehicle. All OBD I vehicles have a universal 1G-pin DLC, with dedicated pin assignments. On pre-OBD Il vehicles, the size of the connector and the number of pins varied, so an adapter may have to be used. If the scan tool is not powered through the DIC, connect the power lead(s) to the cigarette lighter or battery. The scan tool may ask you certain questions to identify the vehicle being serviced. Most scan tool have burtons or knobs with which to input information. Once the vehicle is identified, you can then select the desired diagnostic information. In addition to accessing D'TCs, modern scan tools can also display data stream values. Data-stream values are the electrical operating values of the sensors, actuators and circuits in the computer control system. The displayed values can then be compared with specifications stored in the scan tool or located in the service manual. Some scan tools can also provide "snapshot' data. This allows the technician to check for problems when driving the vehicle. If there is an intermittent or condition-specific problem, the technician can then take a 'snapshot' of the transmission control system, capturing the various sensor readings when the malfunction occurs, The technician can then review the information back at the shop to find the cause of the problem. Some scan tools can be used to perform tests and are known as bidirectional scan tools. The scan tool can activate various switches and actuators and then tell you whether the component is functioning properly. Road Testing Conduct the road test in the same manner described earlier in this study guide, except connect a scan too! to the DLC to monitor engine and transmission function. Record any stored codes that appear during the road test, clear the computer's memory, and then road test the vehicle again. If the DTC(s) reappears after the second road test, it's an indiction that a hard failure exists. ________________________________________________________________________________

ASE 2 - 3.4

Diagnosis And Testing.txt At this point you can refer to the appropriate service information to identify the systems and circuits that the DTCs represent. The diagnostic charts will describe the circuit and the fault that the code represents and contain troubleshooting procedures and rests that must be performed, to determine the cause of the malfunction. These tests usually describe various voltage and resistance measurements using a Digital Multimeter (DMM). If the code(s) does not return, it means that the problem is intermittent. In this case, you can at least use the initially stored DTC(s) as a cue to locating the intermittent failure. Depending on the application, a scan tool can be used to display pertinent information such as sensor input signals, solenoid status (ON or OFF), and commanded gear. A bi-directional scan tool can be used to actuate specific circuits such as TCC and shift solenoids. This is helpful when attempting to isolate problems as being either electrical or mechanical. If the vehicle exhibits transmission problems but does not set any codes, refer to the symptom-driven diagnostic charts contained in most manufacturers' service manuals. Scan tool data-stream values can also be invaluable when there are no codes. Data stream values are the actual electrical values of the transmission control system sensors and actuators measured while the vehicle is operating. These values can then be compared with the manufacturer's specifications. Since a value that is not within spcc should in theory set a DTC, a value that is almost out of spec might not set a DTC but could indicate a problem area. A DTC does not indicate that there is a problem with a particular component but rather that there is a problem in the circuit that includes the component. The problem could be an open circuit caused by a broken wire, high resistance due to dirty, corroded or loose terminals in a connector, or a short circuit caused by worn wiring insulation. The diagnostic information in the manufacturer's code charts will detail the voltage, resistance and current flow checks that should be made to identity the failure. Before concentrating on the circuit, make sure the power and ground connections are good. The voltage at the battery, PCM or TC and transmission power relay (if equipped) should be 12.6 volts with the engine off and 13.6-15.0 volts with the engine running. Voltage drop between the PCM or TCM ground terminal and ground should be 0.2 volts or less. ________________________________________________________________________________

ASE 2 - 3.5

Service Precautions The following precautions should be observed when testing or servicing components and circuits of an electronic transmission control system: � Never disconnect any electrical connector with the ignition switch ON. This creates high voltage spikes, known as short duration transients, which can permanently ruin circuits. � Some electronic transmission control circuits are designed to carry very small amounts of current. For this reason, a high-impedance (over 10 Mega Ohms) digital meter must always be used when troubleshooting computer-related circuits. Always connect the negative lead of a voltmeter first. � Never use a test light unless specifically instructed to do so in the manufacturer's diagnostic procedure. � To prevent damage from electrostatic discharge, always touch a known good ground before handling an electronic component. This is especially important after sliding across a seat or walking a distance. � Do not touch the terminals of an electronic component unless it is necessary, as oil from skin can cause corrosion ________________________________________________________________________________

ASE 2 - 3.6

Electrical Testing In order to perform diagnostic tests, a technician must be able to measure voltage, voltage drop, amperage and resistance using a DMM. Voltage Measurements If there is a DC/AC switch, make sure it is switched to the DC position. Set the function/ range control to the desired volts position. If the magnitude of the voltage is nor known, set the switch to a range that will read the most voltage seen on the vehicle. (Normally, a 20V range will be sufficient). Reduce the range until you have a satisfactory reading. Connect the test leads to the circuit being measured and read the voltage on the display. Resistance Measurements Set the function/range control to the desired position. If the magnitude of the resistance is not known, set the switch to the highest range, then reduce until a satisfactory reading is obtained. If the resistance being measured is connected to a circuit, turn off the power to the circuit being rested. Turn off the ignition. Connect the test leads to the circuit being measured and read the resistance on the display. Voltage Drop Each component in a circuit has some resistance value, and the voltage is reduced as it moves the circuit's resistive loads. The sum of all the voltage drops across a circuit will equal the original amount of applied voltage. Voltage never disappears - it is merely converted into an- TUD other form of energy by the resistance of the load or wires. The voltage available at any point depends on the circuit resistance. The higher the resistance, the more voltage is needed to force current through the circuit. Resistance of any type will use some voltage potential, so the use of voltage is lost across any type of resistance. To measure voltage drop, set the voltmeter switch to the 20-volt position. Connect the voltmeter negative lead to the ground side of the resistance or load to be measured. Connect the positive lead to the positive side of the resistance or load to be measured. Read the voltage drop directly on the 20-volt scale. A high voltage reading is a sign of too much resistance. Conversely, if the voltage drop is too low, then that condition signifies too little resistance. Amperage Measurements An ammeter is connected in series with the circuit, so all the current passing through passes through the ammeter. This means that the fuse must be removed from the circuit, or a connection broken. The ammeter is then inserted into the circuit to replace the fuse or join the two halves of the circuit, observing proper polarity with an analog meter. Connect the ammeter as you would a voltmeter, with the red or positive probe connected on the battery positive side of the circuit, and the negative lead toward the ground side of the circuit or the battery negative terminal. When working on the voltage side of the load, the negative lead would then be on the load side of the ammeter. If working on the ground side, the positive leaf would be on the load side of the ammeter, and the negative lead would then be on the side away from the load. The ammeter should always be set to the highest range before starting to rake a measurement. Then, lower the setting one notch at a time until a usable reading is obtained. If the reading is more than half the scale on an analog ammeter or more than half the digital range on a digital ammeter, don't switch to a lower range. This will protect an analog unit from damage. A digital unit will not be able to give a reading if the amperage measured is out of range. ________________________________________________________________________________

ASE 2 - 3.7

Transmission Control System Sensors, Switches and Actuators

NOTE: Not all transmission control systems will include all components listed here Throttle Position (TP) Sensor The TP sensor is mechanically connected to the throttle shaft of the throttle body assembly. It is a potentiometer, which is a device that changes voltage by varying its internal resistance. One end of the IP sensor's resistance strip is connected to a 5-volt supply from the computer, while the other end of the strip is connected to ground. A third terminal is the signal circuit, and is connected to a movable contact inside the TP sensor. The movable arm acts like a wiper that sweeps the resistance strip as the position of the throttle plate(s) changes. The voltage will vary from approximately 0.5V at dosed throttle, to 4.5V at wide open throttle. The computer converts the signal voltage to a percentage, which it then uses for shift scheduling, transmission line pressure control and CC control. When TP sensor voltage is low (low percentage of throttle opening) mainline pressure will be low and shifts will occur earlier. When TP sensor voltage is high (high percentage of throttle opening) mainline pressure is increased and shifts occur later. If there is a malfunction in the TP sensor circuit, the computer will recognize that she signal is out of specification and then operate the transmission at high mainline pressure to prevent transmission damage. Symptoms of a faulty TP sensor circuit include harsh shift engagements, firm shift feel, abnormal shift schedule, and a TCC that does not engage or cycles. In most cases a fault in the TP sensor circuit will illuminate the MIL. To rest the TP sensor, disconnect the electrical connector and connect the DMM leads (DMM in the ohms position) to the TP sensor signal and ground terminals. Open and close the throttle while observing the DMM. The resistance reading should go from low to high and back again as the throttle is operated. Reconnect the TP sensor connector and turn the DMM to the volts position, then turn the ignition ON. Connect the negative DMM lead to a good ground and use the positive lead to probe the input voltage at the connector. Compare the MM reading with manufacturer's specifications. Move the positive lead to the output voltage terminal and observe the voltage as the throttle is opened and closed. The output voltage should smoothly increase and decrease. ________________________________________________________________________________

ASE 2 - 3.8

Engine Coolant Temperature (ECT) Sensor The coolant temperature sensor is primarily used as an input signal for TCC application. The increased load of the TCC is undesirable when the engine is cold due to the additional load that it places on the engine. The coolant temperature sensor is an NTC (Negative Temperature Coefficient) thermistor installed in the engine's cooling system. It's a two-wire device supplied with a 5-volt signal from the computer. As engine temperature increases, the resistance of the ECT sensor become lower. This action causes a voltage drop at the computer's signal terminal, which is interpreted as higher engine temperature. ECT sensor resistance values versus coolant temperature, range from as high as 100,000 ohms at -40�F, to as low as 100 ohms at 248�F. These numbers translate into voltage readings at the computer's signal line of 5V (-40�5) and approximately IV (248"F) respectively. If there is a fault in the ECT sensor circuit, the TCC may not engage, resulting in reduced fuel economy. The ECT sensor is tested by measuring the resistance of the sensor with the DMM and comparing the reading with the manufacturer's specification for resistance at the sensor's particular temperature. The sensor can also be cooled and heated in water and the resistance readings compared with specifications for various temperatures. Replace the sensor if measurements do not correspond with specifications. ________________________________________________________________________________

ASE 2 - 3.9

Vehicle Speed Sensor (VSS) The vehicle sped sensor is a permanent magnet sensor. The VSS consists of a permanent magnet surrounded by a coil of wire. A toothed ring, also called a reluctor, is located on the transmission's output shaft. The VSS and the reluctor are positioned so that a slight air gap (generally 0.050 in.) is maintained between the two. As the output shaft turns, the reluctor causes the magnetic field of the VSS to continually change from strong to weak. This produces an alternating current output, which increases in both frequency and amplitude as vehicle speed increases. Unlike the TP sensor and ECT sensor, the VSS produces its own voltage. The resistance of the coil windings in the VSS is typically around 1200 ohms, Always check the manufacturer's specification when performing diagnosis. The computer uses the VSS signal to regulate line pressure for shift timing. In addition, the VSS is used as an input for TCC application. A malfunction in the VSS circuit can cause firm shift feel, abnormal shift timing, unexpected down-shifts, no upshifts, no high gear, no engine braking in 2nd or 3rd gears and no TC application. To test the VSS, disconnect the wiring connector from the sensor and connect the leads of a DMM, set on the ohms position, to the sensor terminals. Compare the resistance reading with manufacturer's specifications. High or infinite resistance readings are caused by excessive resistance or possibly an open circuit. If the resistance reading is low there is a short circuit. Next, change the DMM to the AC volts position. Raise and safely support the vehicle so the drive wheels are off the ground. Start the engine and place the gear selector in Drive. Observe the DMM as the engine speed is increased. The voltage reading should increase smoothly as engine speed increases.The VSS can also be checked using a lab scope. In place of the DMM, connect the lab scope leads to the sensor terminals. When the speed is constant, a sine wave pattern should appear on the scope. As speed is increased the AC signal should change in amplitude and frequency. ________________________________________________________________________________

ASE 2 - 3.10

Mass Air Flow (MAF) Sensor The MAF sensor directly measures the mass of the air flowing into the engine. The MAF sensor sends a DC signal ranging from 0.5-5.0 volts to the computer, which in turn uses the information o calculate injector pulse width. For transmission control purposes, the MAF signal is used for mainline pressure control, shift timing and TCC application,A malfunction in the MAF sensor circuit can result in incorrect shift timing, low or high mainline pressure, and incorrect TCC engagement timing. A malfunction in this circuit will also usually illuminate the MIL. You can test the MAF with a DMM or an oscilloscope; refer to the vehicle service manual for specifications. Another method of checking a MAF sensor is to measure the pulse width of the fuel injector. Pulse width is a measurement of how long the fuel injector is open, or how much fuel the fuel injector is delivering. Restrict the air intake and look for a change in fuel control. If a change in fuel delivery is noticed, the MAF sensor is most likely working properly.

ASE 2 - 3.11

Manifold Absolute Pressure (MAP) Sensor The computer sends the MAP sensor a voltage and the sensor varies the voltage according to manifold vacuum. The computer uses the MAP signal to determine engine load. For transmission control purposes, the MAP signal is used for mainline pressure control, shift timing and TCC application. A malfunction in the MAP sensor circuit can result in incorrect shift timing, low or high mainline pressure, and incorrect TCC engagement timing. A malfunction in this circuit will also usually illuminate the MIL There are two types of MAP sensors, the analog signal type and the frequency signal type. Analog signal type sensors can be checked using a DMM. Connect the DMM to the sensor and turn the ignition key ON. If the DMM reading falls in the range of 4.6 to 5.0 volts, the sensor is functioning properly, at this point. Start the engine and let it idle. An idling engine will produce a large amount of intake manifold vacuum, which should pull the MAP' sensor's voltage down to a low reading of approximately one volt (reading will vary with altitude). When the throttle is opened and vacuum drops, the voltage should increase. This test indicates that the MAP sensor is responding to vacuum. Check the service manual for the specifications for the vehicle you are testing, Frequency signal type MAP sensors can be tested with a digital tachometer. A tachometer is a frequency counter. Ir measures pulses received per second (Hz) and converts them to rpm. The frequency should be high when vacuum is low and low when vacuum is high. Always refer to the vehicle service manual for the exact values and testing procedures.

ASE 2 - 3.12

Transmission Range (TR) Sensor) The TR sensor receives a voltage signal from the computer. The TR sensor incorporates a series of resistors that reduce the voltage according to the various transmission ranges. When the TR sensor circuit is operating properly, the voltage signal that is returned to the computer corresponds to the position of the transmission range selector lever (P,R, N, D, 2, 1). The TR sensor signal is used to determine the desired gear and for mainline pressure control. A malfunction in the TR sensor circuit can result in harsh shift engagement and firm shift feel. It can also cause a no-crank condition. The TR sensor can be tested using a DMM set in the ohms position. Connect the leads to the proper terminals and move the TR sensor into each gear position. Record the resistance readings and compare with manufacturer's specifications.

ASE 2 - 3.13

Transmission Fluid Temperature (TFT) Sensor The TFT sensor is a NTC thermistor used to sense the temperature of the transaxle fluid. The sensor is located in the transmission oil pant. The computer uses the IFT sensor signal to delay shift points when the transmission fluid is cold, control line pressure and to control operation of the TCC. A malfunction in the FT sensor circuit can result in improper TCC operation and incorrect line pressure. The TFT sensor is tested by measuring the resistance of the sensor with a DMM and comparing the reading with the manufacturer's specification for resistance at the sensor's particular temperature. The sensor can also be cooled and heated in water and the resistance readings compared with specifications for various temperatures. Replace the sensor if measurements do not correspond with specifications.

ASE 3 - 3.14

Turbine Shaft Speed (TSS) Sensor The TSS sensor is a magnetic pickup that senses the rotation of the torque converter turbine shaft (input shaft). The TSS signal increases in frequency as input shaft speed increases. This signal is used by the computer to control CC operation and to determine line pressure during shifts. A malfunction in the TSS sensor circuit can result in no TC engage-mentor harsh shifts. The resistance of the TSS sensor can be rested using a DM. Record the resistance reading and compare with manufacturer's specifications.

ASE 2 - 3.15

Brake On/Off (BOO) Switch.txt The BOO switch signals the computer when the brakes are applied. The switch is closed when the brake pedal is depressed and open when it is released. The switch disengages the CC when the brakes are applied Depending on how the switch fails, the TCC may either not engage of not disengage. Check for voltage at the switch. If there is no voltage, check the fuse and wiring. If voltage is present, activate he switch and check for voltage on the opposite side of the switch. If voltage is not present, replace the switch assembly, Torque Converter Clutch To rest TCC operation, drive the vehicle at 40-50 mph with light application of the throttle (cruise). Lightly tap the brake pedal, just enough to rum on the brake lights but not enough to apply the brakes, and feel for a soft downshift accompanied by a slight increase in engine speed, indicating that the TCC has released. Release the brake pedal, slowly accelerate and check for reapply of the TCC and a slight decrease in engine rpm. If the CC released and reapplied, it is operating properly. However, if nothing happened, there is a malfunction in the TCC hydraulic or electronic control circuits. Most TCCs are controlled by the PCM or TCM and if there is a malfunction in the electronic control circuit, it should set a DTC. Refer to the manufacturer's service information for electrical test values for the TCC circuit. The TCC hydraulic circuit can be tested using a 100-psi pressure gauge teed into the transmission-to-cooler line at the radiator. Route the hose out from under the vehicle so it is in view of the driver and not contacting any hot or sharp engine components. Raise and safely support the vehicle so that the drive wheels are off the ground. Observe the pressure gauge and apply the accelerator with the transmission in Drive range until the 2-3 upshift occurs and the indicated speed is approx. 50 mph. If the TCC control valve is operating, there should be a momentary drop of 5-10 psi on the gauge. If the pressure changed but the TCC did not apply, there is a problem with the torque converter or transmission input shaft. If the pressure did not change, there is a problem with the TCC valve, solenoid or electronic control circuit.

ASE 2 - 3.16

Torque Converter Clutch To test TCC operation, drive the vehicle at 40-50 mph with light application of the throttle (cruise). Lightly tap the brake pedal, just enough to rum on the brake lights but not enough to apply the brakes, and feel for a soft downshift accompanied by a slight increase in engine speed, indicating that the TCC has released. Release the brake pedal, slowly accelerate and check for reapply of the TCC and a slight decrease in engine rpm. If the CC released and reapplied, it is operating properly. However, if nothing happened, there is a malfunction in the TCC hydraulic or electronic control circuits. Most TCCs are controlled by the PCM or TCM and if there is a malfunction in the electronic control circuit, it should set a DTC. Refer to the manufacturer's service information for electrical test values for the TCC circuit. The TCC hydraulic circuit can be tested using a 100-psi pressure gauge teed into the transmission-to-cooler line at the radiator. Route the hose out from under the vehicle so it is in view of the driver and not contacting any hot or sharp engine components. Raise and safely support the vehicle so that the drive wheels are off the ground. Observe the pressure gauge and apply the accelerator with the transmission in Drive range until the 2-3 upshift occurs and the indicated speed is approx. 50 mph. If the TCC control valve is operating, there should be a momentary drop of 5-10 psi on the gauge. If the pressure changed but the TCC did not apply, there is a problem with the torque converter or transmission input shaft. If the pressure did not change, there is a problem with the TCC valve, solenoid or electronic control circuit.

ASE 2 - 3.17

Transmission Solenoids The transmission actuators controlled by the PCM or TCM are usually electric solenoids, such as the TCC solenoid and the shift solenoids. A solenoid is basically a coil of wire that becomes an electromagnet when current flows through it. It then loses its magnetism when the current flow is turned off. The solenoid contains an iron plunger inside the wire coil that is spring loaded to one position. When the solenoid is energized, the plunger moves to the other position. The plunger movement in turn opens or closes a hydraulic valve. Solenoids can be normally closed and opened when activated or normally open and closed when signaled. The resistance and mechanical operation of electric solenoids can be checked. To check resistance, disconnect the wiring connector from the solenoid and connect the DMM leads to the solenoid terminals. Compare the resistance reading on the DMM with manufacturer's specifications. Then move one of the DMM leads to the solenoid body or base to check for a ground circuit. A two-wire solenoid will not be grounded through the solenoid case, so the DMM reading should be infinity. A single wire solenoid is grounded through the solenoid case, so in this case there should be continuity. The mechanical operation of a solenoid can be tested by blowing air through it when it is energized and de-energized. A normally closed solenoid should allow air to pass when energized but block air flow when it is not energized. A normally open solenoid should allow air to pass when it is not energized but block air flow when it is energized.

4.0 Transmission/Transaxle Maintenance and Adjustment

A2 4.1 - Fluid and Filter Change

WARNING: The transmission fluid will be very hot during this procedure. Wear eye and skin protection to prevent injury, Some vehicle manufacturers recommend that the transmission fluid and filter be changed at specified intervals. These intervals are routinely shortened when the vehicle is used under severe driving conditions. These conditions usually include frequent trailer towing, stop-and-go driving in hot weather, operating in hilly terrain or commercial, police or tad use. See the maintenance guide for the vehicle being serviced for the fluid change interval. To change the transmission fluid, first bring the transmission to normal operating temperature, then raise and safely support the vehicle. Position a suitable drain pan under the transmission oil pan. Some transmission oil pans do not have drain plugs, so the pan must be removed to drain the fluid. Start removing the pan retaining bolts, beginning at the end of the pan from where the fluid will first begin to drain. Working towards the other end of the oil pan, remove the pan bolts from each side of the pan, allowing the pan to tilt and the fluid to begin to drain. Remove all but two bolts at the opposite end of the pan from where the fluid is draining If the oil pan has not come loose at this point, tap on the sides of the pan with a mallet until it breaks free.Loosen the two remaining bolts until the pan lowers enough to allow all remaining fluid to drain. Support of burned lining material from a slip ping clutch or band. If the pan and the lower part of the transmission case and valve body have a varnish like appearance and odor, this is evidence that the transmission run hot. Thoroughly clean the debris and old gasket material from the oil pan, magnet and transmission case. Inspect the pan flange for distorted bolt holes caused by over tightening the pan bolts. If the holes are distorted, place the flange on a flat surface pan, remove the two bolts and remove the pan from the vehicle. Remove the transmission filter fastener(s) and remove the filter and filter neck O-ring or gasket. Inspect the pan, filter and pan magnet. A small amount of metal particles, along with blackish oil film is considered normal; the metallic particles are probably from break-in and normal wear. However, large amounts of metal indicates excessive wear or damage to gears, bearings, thrust washers, etc. If the pan contains loose black material that smells burned, this is evidence face and tap down the raised area with a hammer. If the pan bolts use compressible conical washers, any bolts with the washers reversed must be replaced. Install a new filter using a new gasket or O-ring and secure it with the fastener(s). Install the oil pan, using a new gasket, and tighten the bolts, in a criss-cross pattern, to the specified torque, Lower the vehicle and fill the transmission with the proper type and quantity of fluid. Check the fluid level as described in the General Transmission/ Transaxle Diagnosis section of this study guide. Road test the vehicle and check for leaks.

ASE 2 - 4.1

MANUAL SHIFT LINKAGE

NOTE: An inspection of manual shift linkage operation is detailed in the General Transmission Transaxle Diagnosis section of this study guide. Removal and Installation The manual shift linkage consists of a series of rods and levers or a cable that connects the gear selector to the lever on the outside of the transmission. If equipped with linkage rods, check the linkage for obvious damage like cracked, broken or bent rods and worn bushings. Have an assistant move the gear selector while you watch the movement of the linkage. Look for signs of abnormal movement or a rod or lever moving significantly before its corresponding component moves, which would indicate wear in the pivot. Check cables for fraying, kinks or other damage. Use new clips when replacing rod linkage components, as required. If a bushing is worn or missing and the link is grooved from wear or the pivot hole is elongated, don't just install a new bushing, replace the worn part as well as the bushing. Lubricate linkage pivot points as required, and properly adjust the linkage once component replacement is completed. Cables are usually attached with clips or snap-in to brackets. Replacement is accomplished by disconnecting the cable from the transmission and gear selector levers and disconnecting the cable housing from the brackets, then routing the cable through the floor or firewall. Adjustment NOTE: The following is a general procedure for manual shift linkage adjustment. Always refer to the vehicle service manual for the exact adjustment procedure. Place the gear selector lever in Park, then raise and safely support the vehicle. Loosen the linkage adjustment. This may involve loosening a nut or bolt that secures a threaded rod, adjustment swivel or slotted shift rod or cable. Place the transmission lever in Park. To ensure that the transmission is in the Park position, try to move the driveshaft. The parking pawl is engaged if the driveshaft does not move. Tighten the clamping nut or bolt, then check linkage operation as described in the General Transmission/Transaxle Diagnosis section of this study guide.

ASE 2 - 4.2

5.0 In-Vehicle Transmission/Transaxle Repair

DRIVE AXLE BUSHINGS AND SEALS

A2 5.1

Transmission Bushing And Seal Replacement

A2 5.2

Transmission Extension Housing Removal and Installation

A2 5.3

Transaxle Differential Seal Replacement

A2 5.4

Transmission Cooler Service

A2 5.5

Speedometer/Speed Sensor Gears

A2 5.6

Valve Body - Removal

A2 5.7

Valve Body - Cleaning and Inspection

A2 5.8

Valve Body - Installation

A2 5.9

Servos and Accumulator

A2 5.10

Powertrain Mounts

6.0 Off-Vehicle Transmission/Transaxle Repair

A2 6.1

Transmission Removal

A2 6.2

Transmission Installation

A2 6.3

Transaxle Removal

A2 6.4

Transaxle Installation

A2 6.5

Transmission Overhaul

A2 6.6

Transmission Overhaul - Torque Converter

A2 6.7

Transmission Disassembly

A2 6.8

Cleaning Inspection and Repair

A2 6.9

Oil Pump

A2 6.10

Bearing Preload

A2 6.11

Thrust Washers and Bearings

A2 6.12

Bushings

A2 6.13

Transmission Seals

A2 6.14

Transmission Shafts

A2 6.15

Planetary Gears

A2 6.16 - Transmission Case

A2 6.17 - Clutches

A2 6.18 - Bands

A2 6.19 - One-Way Clutches

A2 6.20 - Transaxle Differential

A2 6.21 - Transmission Assembly

Q1. Engine cylinder pressure should be within __% of each other. Q2. A good cylinder leak-down test reads no more than __%. Q3. Blue smoke on acceleration usually means: Q4. The camshaft is driven by the crankshaft via: Q5. PCV valve stuck closed causes: Q6. Crankshaft end-play is checked with a: Q7. A noisy timing chain is usually caused by a worn: Q8. Oil pressure should rise immediately when the engine: Q9. The oil pump is driven by the: Q10. A collapsed lifter causes:

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