Note. AT failures most often occur for one of the following five reasons: reduced engine output efficiency, misadjustments, hydraulic failures, mechanical damage, or on-board processor/signal circuit failures. Failure diagnosis should always start with the simplest checks: check the level and condition of the ATF (see chapter Settings and ongoing maintenance), check the adjustment of the shift cable and transmission position switch. Next, test drive the vehicle to determine the effectiveness of the corrections made. If the problem cannot be fixed, you should drive the car 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 the diagnosis of failures of vehicle components and systems at the beginning of this Guide.
Primary Checks
1. Warm up the transmission to normal operating temperature for a short drive.
2. Check the ATF level (see chapter Settings and ongoing maintenance):
- a) If the liquid is clearly not enough, make the appropriate adjustment by adding the required amount of fresh ATF. Verify that the dipstick adjustment is correct, then check the transmission for signs of external leaks (see below);
- b) If the level is too high, drain excess ATF, then check it for signs of coolant presence, indicating a leak in the internal bulkheads of the radiator separating its heat exchanger from the side tanks with ATF (see chapter Cooling, heating systems);
- c) If the ATF is foamy, empty the transmission and fill it with fresh fluid - check the drained one for signs of coolant presence.
3. Check the engine idle speed setting. Note: If the engine is out of order, do not proceed with the initial checks of the transmission until the appropriate corrections have been made.
4. Check the freedom of movement of the throttle control cable (see chapter Power and exhaust systems)
5. Check shift cable pull (see Section Removal and installation of the switching lever (selector) gear), make sure that the adjustment is correct and that it can move freely.
Diagnosis of ATF leaks
Most leaks are easily identified by visual inspection. Repair usually consists of replacing the corresponding defective oil seal or gasket. If the external inspection fails to identify the source of the leak, proceed as described below.
First of all, the possibility of error in determining the nature of the leak should be excluded. ATF should not be confused with engine oil or brake fluid (transmission fluid is usually dark red in color).
Run a short test to find the source of the leak (several kilometers) ride, then park the car over a blank 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 special attention to the joint of the mating gasket surfaces. In order to expand the viewing angle, use a pocket mirror.
If you still cannot find the source of the leak, carefully wipe the surface of the suspected area with a rag soaked in solvent, then dry it.
Make another short drive, this time changing your speed frequently, then re-examine the cleared suspect area.
After identifying the source of the leak, it is necessary to determine and eliminate the cause of its development, and only then proceed to perform the necessary restoration work. Replacing a damaged gasket will not produce the desired result if the mating surface defect that caused the gasket failure is left unrepaired. So, the 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 driven to a service station.
Leakage through gasket surfaces
Periodically inspect the cover on the right side of the transmission case. Check that the fixing bolts are in place and securely tightened, make sure that there are no signs of mechanical damage on the cover.
Possible causes of cover leaks include overtightening of mounting bolts, damage to the transmission case sealing surface, gasket failure, and cracked or porous case walls. If the gasket of the cover or transmission case is formed by a sealant pad, the possibility of an incorrect choice of the type of the latter cannot be ruled out.
Leaks through glands and cuffs
The most typical causes of failure of transmission oil seals include an excessively high level of ATF, a violation of the patency of the ventilation breather, mechanical damage to the walls of the seat, damage to the oil seal itself, or improper installation of the latter. It is also possible that the trunnion of the shaft threaded into the stuffing box is damaged, or the latter has excessive play as a result of bearing wear.
Check the condition and correct fit of the sealing collar of the dipstick guide tube. Periodically inspect the surface around the speedometer drive gear or speed sensor for signs of leaks (VSS). If necessary, replace the sealing ring.
Leaks through defects in the walls of the transmission case
The reason for the development of ATF leaks may be the formation of cracks or pores in the body of the transmission case. Consult with car service specialists.
Check the tightness of the union connections of the ATF cooler hoses.
Leaks through the breather and filler neck
Breather or filler leaks can result from overfilling the transmission, coolant in the ATF, or a blocked breather or return port.