Contents: Preliminary diagnostics ↧ Checking for transmission fluid leaks ↧ Leak through the gasket ↧ Leakage through seals ↧ Leak through the casing ↧ Fluid leaking from dipstick tube or… ↧
Note: Automatic transmission failures may occur due to the following reasons: reduced engine performance, incorrect adjustments, hydraulic system problems, mechanical failures, as well as processor circuit failures or malfunctions. Diagnostics should begin with the most simple tests: checking the condition and level of transmission fluid (see chapter 1), as well as checking the correct adjustment of the selector cable (see subsection 3). After this, a test run should be carried out. If the problem is not resolved, continue diagnostics. If the cause of the malfunction is not determined after performing preliminary diagnostics, provide the vehicle to qualified service and repair station specialists. In the section "Determining the causes of malfunctions" a description of the symptoms of problems that occur with an automatic transmission is provided.
Preliminary diagnostics
1. Drive the vehicle until the transmission fluid warms up to normal operating temperature.
2. Check the fluid level as described in chapter 1:
- a) If the level is below normal, add transmission fluid until the level rises to the normal mark on the dipstick. Make sure there is no fluid leakage from the box.
- b) If the level is above normal, drain the excess transmission fluid and check it for contamination with coolant. The presence of coolant in the transmission fluid of an automatic transmission indicates a leak in the heat exchanger, the walls of which separate the coolant and transmission fluids (see chapter 3).
- c) If foaming of the transmission fluid is observed, drain and refill the transmission, then check that there is no coolant in the transmission oil and that the transmission fluid level does not exceed the required level.
3. Make sure that the engine idle speed is normal.
Note: If during the check any malfunctions in the engine operation are detected, further preliminary diagnostics of the gearbox should be stopped and the malfunctions in the operation of the power unit should be eliminated.
4. Inspect and adjust the shift cable (see subsection 3).
5. Make sure the Park/Neutral (PNP) position switch is adjusted correctly (see subsection 5).
Checking for transmission fluid leaks
6. Often, transmission fluid leaks can be detected by visual inspection. Fixing this problem typically involves replacing the seal or gasket. If the source of the leak cannot be determined by inspection, perform the following procedure.
7. Determine the type of leaking liquid. Make sure that it is transmission fluid that is leaking, and not engine oil or brake fluid (automatic transmission fluid has a deep red color).
8. Try to pinpoint the source of the leak. Take a drive, then leave the car with a large piece of cardboard underneath it. After one or two minutes, the source of the leak should be determined by the location of the liquid traces on the sheet.
9. Carefully inspect the element that may have a leak, as well as the surrounding area. Pay special attention to the seals of the mating surfaces. To inspect hard-to-reach areas, it is recommended to use a mirror.
10. If the above checks fail to locate the source, thoroughly clean the suspected leak area with solvent and dry.
11. Drive the vehicle for several kilometers within the normal engine operating temperature range and in various gears. After the run, re-inspect the element that may be the source of the leak.
12. Once you have identified the location of the leak, before fixing it, determine and fix its cause. If the connecting flange is deformed, then after installing a new gasket the leak may not stop - first you need to align the flange.
13. Before attempting to repair a leak, make sure there is no leak in the locations listed below.
Note: It may not be possible to detect leaks in the locations listed below without specialized equipment and specific diagnostic procedures. In this case, you should contact a service station with the appropriate level of competence and equipment.
Leak through the gasket
14. Inspect the tray periodically. Make sure all bolts are present and tight, that the gasket is not damaged and that there are no significant dents on the surface of the pan (dents on the pallet may cause damage to the valve body, which is located inside).
15. Causes of leakage through the gasket may be excessively high level and pressure of transmission fluid, clogged channels, excessive tightening of the pan bolts, deformation of the pan connecting flange, damage to the mating surface of the gearbox housing, damage to the gasket or flange of the gearbox housing. A leak can also occur due to the use of an incorrect type of sealant to seal the connection between the engine sump and the gearbox housing.
Leakage through seals
16. Causes of seal leakage may include excessively high transmission fluid level and pressure, clogged passages, damage to the seal seat, improper installation or damage to the seal, as well as damage to the shaft surface in contact with the seal, or excessive clearances in the bearings, which leads to excessive shaft runout.
17. Make sure that the oil dipstick tube is installed correctly and that its seal creates a tight seal. Periodically check the area around the drive gear or speedometer sensor for signs of transmission fluid leakage. If the inspection reveals oil leaks, inspect the oil seal.
Leak through the casing
18. If the transmission housing is confirmed to be leak-proof, this housing part should be restored or replaced.
19. Check that the oil cooler hose connectors are intact and secure. If a leak is detected, the first thing to inspect is the O-rings on the transmission oil cooler line couplings.
Fluid leaking from dipstick tube or vent tube
20. Causes of leakage may include overfilling of the gearbox, presence of coolant in the transmission oil, cracking of the gearbox casing, use of the wrong type of dipstick, as well as clogging of the ventilation tube or oil return circulation channels.