Table of contents: Primary checks ↓ ATF Leak Diagnosis ↓ AT diagnostic trouble codes ↓ Clearing CPU memory from codes ↓
AT failures most often occur for one of the following five reasons:
- a) Reduced engine output efficiency;
- b) Violation of regulations;
- c) Hydraulic failure;
- d) Mechanical damage;
- e) Failures of the on-board processor/its signal chain.
Failure diagnostics should always start with the most basic checks: assess the level and condition of the ATF (see Chapter Settings and ongoing maintenance), check the adjustment of the gearshift and throttle actuators. Next, conduct a road test of the vehicle to determine the effectiveness of the corrections made. If the problem cannot be resolved, the vehicle should be taken to a service station for more detailed diagnostics using special equipment. A description of some of the symptoms of AT failures is given in the Section on Diagnostics of Failures of Vehicle Components and Systems at the beginning of this Manual.
Primary checks
1. Warm up the transmission to normal operating temperature by taking it for a short drive.
2. Check the ATF level (see Chapter Settings and ongoing maintenance):
- a) If the fluid is clearly low, make the appropriate adjustment by adding the required amount of fresh ATF. Check the dipstick to make sure the adjustment is correct, then check the transmission for signs of external leaks (see below);
- b) If the level is excessively high, drain the excess ATF, then check it for traces of coolant, indicating a leak in the internal radiator bulkheads separating its heat exchanger from the side ATF tanks (see Chapter Cooling and heating systems);
- c) If the ATF is foamed, drain the transmission and fill it with fresh fluid, - check the drained ATF for traces of coolant.
3. Check the engine idle speed setting (see Chapter Power and exhaust systems). If necessary, take the vehicle to a service station to have the appropriate adjustments made.
Note: If the engine is not in good condition, do not proceed with the initial transmission checks until the appropriate corrections have been made.
4. Check the freedom of movement of the gearshift control cable (see section Checking, adjusting and replacing the gear shift cable), make sure that the adjustment is correct and that the rod runs smoothly.
ATF Leak Diagnosis
General information
Most leaks are easily identified by visual inspection. Repair usually consists of replacing the affected seal or gasket. If the source of the leak cannot be identified by visual inspection, proceed as described below.
First of all, it is necessary to exclude the possibility of an error in determining the nature of the leak. ATF should not be confused with engine oil or brake fluid (transmission fluid is usually dark red in color).
To identify the source of the leak, perform a short (several kilometers) drive, then park the car over a clean sheet of cardboard. After a couple of minutes, the source of the leak can be identified by traces of liquid dripping onto the cardboard.
Carefully inspect the suspected area and its surrounding surface, paying particular attention to the joints of the mating gasket surfaces. Use a pocket mirror to widen the viewing angle.
If the source of the leak still cannot be identified, thoroughly wipe the surface of the suspected area with a rag soaked in solvent, then dry it.
Take another short drive, this time changing speed frequently, then re-inspect the cleared suspect area.
After identifying the source of the leak, you should determine and eliminate the cause of its development, and only then proceed to perform the necessary restoration work. Replacing a damaged gasket will not lead to the desired result if the defect of the mating surface that led to the failure of the seal is left unrepaired. Thus, a deformed flange must be straightened.
The following subsections list the most common causes of ATF leaks and the conditions that must be met to prevent recurrence.
Note: Some of the listed requirements cannot be met without the use of special equipment. In this case, the car should be taken to a service station.
Leaks through gasket surfaces
Periodically inspect the transmission oil pan. Check that the mounting bolts are in place and securely tightened, and make sure that there are no signs of mechanical damage on the cover (deformation of the pallet can lead to failure of the valve assembly located inside the transmission).
Possible causes of sump leaks include overtightening of mounting bolts, damage to the sealing surface of the transmission housing, gasket failure, and cracks or porosity in the housing walls. If the sump or transmission housing gasket is formed by a sealant cushion, the incorrect type of sealant may have been selected. Leaks through the sump gasket may also be caused by overfilling the housing with transmission fluid or by increased ATF pressure.
Leaks through seals and cuffs
The most common causes of transmission seal failure include excessively high ATF levels, obstruction of the ventilation pipe, mechanical damage to the walls of the seat, damage to the seal itself, or improper installation of the latter. It is also possible that the journal of the shaft inserted into the seal is damaged, or that the latter has excessive play due to bearing wear.
Check the condition and correct fit of the sealing sleeve of the probe guide tube. Periodically inspect the surface near the speedometer/speed sensor (VSS) drive gear for signs of leaks. Replace the O-ring if necessary.
Leaks through defects in the walls of the transmission housing
The cause of ATF leaks may be the formation of cracks or pores in the transmission housing. Consult with car service specialists.
Check the tightness of the ATF cooler hose connection fittings.
Leaks through the breather and filler neck
Breather or filler neck leaks can occur due to overfilling the transmission, coolant in the ATF, a blocked breather/vent or return drain holes.
AT diagnostic trouble codes
The on-board processor responsible for the functioning of the AT constantly monitors any violations occurring in the system (including circuits of information sensors and actuators). When a fault is detected, a corresponding diagnostic code is entered into the control unit memory. At a service station, the fault codes entered into the processor memory can be retrieved using a device known as "CONSULT" or scanner-type readers. The car owner can read the codes himself using the signals displayed by the "OD OFF" control lamp on the car's instrument panel.
Models produced in 1993 and 1994.
1. Start the engine and warm it up to normal operating temperature.
2. Turn the ignition key to the OFF position.
3. Set the AT operating mode selector to the AUTO position.
4. Turn the overdrive mode switch to the ON position.
5. Move the selector lever to position "P".
6. Without starting the engine, turn on the ignition.
7. The OD OFF indicator light should come on for approximately two seconds:
- a) Failure to turn on the lamp indicates a malfunction of the AT operation control processor (first, make sure that the lamp itself is not broken). The authors of this Manual do not recommend measuring the resistance and voltage at the processor terminals, since random voltage surges/passing excessively high current through the control unit can disable the latter. Take the car to a service station for inspection.
- b) If the OD OFF indicator lamp lights normally, proceed to the next check step.
8. Turn off the ignition.
9. Move the selector lever to position "D".
10. Disengage the overdrive by turning the mode switch to the OFF position.
11. Without starting the engine, turn on the ignition.
12. At least two seconds after turning on the ignition, move the selector lever to position "2".
13. Turn the switch to the ON position to engage the overdrive gear.
14. Move the selector lever to position "1".
15. Turn off the upshift mode (OFF).
16. Press the gas pedal all the way down, then release it.
17. Now the processor should go into the information output mode. Reading of the fault codes stored in the memory of the block can be done by flashing the OD OFF control lamp.
Models from 1995 to 1997.
1. Start the engine and warm it up to normal operating temperature.
2. Turn off the ignition and wait at least five seconds before starting the procedure.
3. Turn the ignition key to the ACC position
4. Turn the overdrive mode switch to the ON position.
5. Move the selector lever to position "P".
6. Without starting the engine, turn on the ignition.
7. The OD OFF indicator light should come on for approximately two seconds:
- a) Failure to turn on the lamp indicates a malfunction of the AT operation control processor (first, make sure that the lamp itself is not broken). The authors of this Manual do not recommend measuring the resistance and voltage at the processor terminals, since random voltage surges/passing excessively high current through the control unit can disable the latter. Take the car to a service station for inspection.
- b) If the OD OFF indicator lamp lights normally, proceed to the next check step.
8. Turn off the ignition.
9. Turn the ignition back on without starting the engine.
10. Move the selector lever to position "D".
11. Disengage the overdrive by turning the mode switch to the OFF position.
12. Without starting the engine, turn on the ignition.
13. At least two seconds after turning on the ignition, move the selector lever to position "2".
14. Turn the switch to the ON position to engage the overdrive gear.
15. Move the selector lever to position "1".
16. Turn off the upshift mode (OFF).
17. Press the gas pedal all the way down, then release it.
18. Now the processor should go into the information output mode. Reading of the fault codes stored in the memory of the block can be done by flashing the OD OFF control lamp.
Models produced in 1998 and 1999.
1. Start the engine and warm it up to normal operating temperature.
2. Turn off the ignition and wait at least five seconds before starting the procedure.
3. Move the AT operating mode selector to the "P" position.
4. Without starting the engine, turn on the ignition.
5. The OD OFF indicator light should come on for approximately two seconds:
- a) Failure to turn on the lamp indicates a malfunction of the AT operation control processor (first, make sure that the lamp itself is not broken). The authors of this Manual do not recommend measuring the resistance and voltage at the processor terminals, since random voltage surges/passing excessively high current through the control unit can disable the latter. Take the car to a service station for inspection.
- b) If the OD OFF indicator lamp lights normally, proceed to the next check step.
6. Turn off the ignition.
7. Turn the ignition key to the ACC position.
8. Move the selector lever to position "D".
9. Without starting the engine, turn on the ignition.
10. Disable overdrive mode (press the switch button to the OFF position), then turn the ignition off and back on. Release the upshift switch (the lamp should go out).
11. At least two seconds after turning on the ignition, move the selector lever to position "2".
12. Press the upshift selector button and, while holding it down, move the selector lever to position "1".
13. Disengage the overdrive (the lamp should go out).
14. Press the gas pedal all the way down, then release it.
15. Now the processor should go into the information output mode. Reading of the fault codes stored in the memory of the block can be done by flashing the OD OFF control lamp.
All models
1. If all monitored circuits are functioning properly, the test lamp will flash one long time, then ten short flashes at equal intervals between them.
2. The start of the countdown of each code is marked by one long flash, followed by ten consecutive flashes, which determine the code number itself:
- a) If the first flash of ten significant ones is long, then there is a fault in the speed sensor circuit;
- b) A long second blink indicates a failure in the VSS circuit;
- c) The third long flash corresponds to a failure in the TPS circuit;
- d) Fourth - in the circuit of the electromagnetic valve of gear shifting A 4
- e) Fifth - in the circuit of the electromagnetic valve of gear shift B;
- f) Sixth - in the circuit of the electromagnetic valve-switch of the overrunning clutch;
- g) Seventh - in the circuit of the electromagnetic valve-switch of the rotation converter clutch;
- h) Eighth - in the ATF temperature sensor circuit;
- i) Ninth - in the engine speed signal circuit;
- j) Tenth - in the circuit of the electromagnetic valve of pressure in the tract;
- k) Alternating long flashes with long eclipses of the control lamp indicates a low battery level;
- l) On models up to 1998, failure of the OD OFF indicator lamp to come on indicates a malfunction of the start/reverse light enable switch, overdrive switch, or TPS;
- m) On 1999 models, failure of the lamp to turn on is usually due to a failure of the Start/Reverse Light Switch Sensor, or TPS.
3. Elimination of faults identified during the inspection requires high qualifications from the performer and should be entrusted to car service specialists. The only exception is the repair/replacement of VSS and TPS (see Chapter Engine management systems).
Clearing CPU memory from codes
1. Clearing the processor memory is one of the repair procedures performed by service station specialists. If the codes were read and the necessary corrections were performed by the car owner himself, proceed in the following order:
2. Turn off the ignition (if it is enabled), wait at least five seconds and turn it on again.
3. Perform the trouble code reading procedures (see above).
4. Turn the selector on the control module (PCM) to switch the system from Mode II to Mode I (see Chapter Engine management systems).