Note: Automatic transmission failure can be attributed to five main causes: poor engine performance, incorrect adjustment, hydraulic failure, mechanical failure, or failure of the computer or its signal network. Diagnosis of these faults should always begin with the easily repairable items: fluid level (Chapter 1), shift linkage adjustment. Then road test the vehicle and determine whether further diagnostics are necessary. If problems persist after the preliminary check, further diagnostics should be performed by a specialist. Information on signs of transmission failure is provided in the section "Troubleshooting" at the beginning of this guide.
Preliminary checks
1. Warm up the gearbox while driving to normal operating temperature.
2. Check the working fluid level as described in Chapter 1:
- a) If the working fluid level is too low, restore it to normal, then check for leaks from the outside.
- b) If the fluid level is too high, drain the excess and then check for coolant in the transmission fluid. The presence of engine coolant in the transmission fluid means that the internal walls of the radiator separating these fluids have been punctured (see Chapter 3).
- c) If the working fluid is foamed, drain it and refill it into the gearbox, then check the fluid level or the presence of engine coolant in it.
3. Check the engine idle speed.
Note: If the engine is faulty, do not proceed with the preliminary checks until the fault has been corrected.
4. Check the throttle control cable for smooth movement. Adjust if necessary (see section 6).
Note: The throttle control cable may work fine when the engine is off and cold, but may stick when the engine is warm. Check the cable operation with the engine cold and warm.
5. Check the gear shift lever mechanism (see section 5). Make sure it is adjusted correctly and runs smoothly.
Diagnostics of working fluid leaks
6. Leaks are usually easy to spot visually. Repairs usually involve replacing seals or gaskets. If the leak location is difficult to locate, the following procedure can be used.
7. Make sure that the leaking fluid is the gearbox working fluid, and not engine oil or brake fluid (the automatic transmission working fluid has a rich red color).
8. Try to locate the leak. Drive the car for a few kilometers, then park it over a large sheet of cardboard. After a few minutes, you will be able to locate the leak by the drips.
9. Carefully inspect the suspicious elements and the area around them. Pay particular attention to the sealed surfaces. Use a mirror to inspect inaccessible areas.
10. If the leak location is still not found after this, thoroughly clean the suspected areas with solvent and dry.
11. Drive the car at normal operating temperature of the gearbox for several kilometers at different speeds. After that, carefully inspect the suspicious areas again.
12. After the leak has been located, the cause must be determined before repairs can be made. If a new gasket is installed and the sealing surface is bent, the seal will not be ensured. The bent flange must be straightened.
13. Before starting repairs, check that the following conditions are met:
Note: Some of the reasons listed below cannot be eliminated without special tools. Such work should be entrusted to specialists.
Leaks through gaskets
14. Check the pan periodically. Check that all bolts are present and tight, and that the gasket and sealing surface are in good condition (dents in the pan may indicate damage to the valve body installed inside).
15. If the oil pan gasket does not provide a seal, the cause may be too high a fluid level or pressure, clogged vent, oil pan bolts are too tight, the oil pan sealing flange is warped, the transmission sealing surfaces are damaged, or the gasket or transmission housing is damaged. If a sealant is used instead of a gasket, the leak may be caused by using the wrong type of sealant.
Leaks through cuffs
16. If the gearbox cuff does not provide a seal, this may be due to too high a level of working fluid or increased pressure, clogged ventilation ducts, damage to the cuff seat, damage to the cuff itself or its incorrect installation, damage to the shaft on which the cuff is placed, or a worn bearing that causes large shaft play.
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17. Check that the fluid level gauge tube seal and its mount are in good condition. Periodically check for leaks around the speedometer and sensor drive gear. If fluid leaks are visible, check the integrity of the O-ring seal. Also check the drive shaft seals for leaks.
Crankcase leaks
18. If the crankcase itself does not provide a seal, then pores have formed in it, so the crankcase must be repaired or replaced.
19. Check the tightness and condition of the oil cooling system hose fittings.
Working fluid is leaking from the vent tube or filler tube
20. This may be due to overfilling of the gearbox, coolant entering the gearbox, crankcase leaks, incorrect installation of the dipstick, clogging of the ventilation channel or drain holes.