Diagnosis – general

Note: Automatic transmission malfunctions may be caused by five general conditions: poor engine performance, incorrect adjust­ments, hydraulic malfunctions, mechanical malfunctions or malfunctions in the computer or its signal network. Diagnosis of these prob­lems should always begin with a check of the easily repaired items: fluid level and condition (see Tune-up and routine maintenance), shift cable adjustment and, if equipped, Throttle Valve (TV) cable adjust­ment. Next, perform a road test to determine if the problem has been corrected or if more diagnosis is necessary. If the problem persists after the preliminary tests and corrections are completed, additional diagnosis should be done by a dealer service department or transmission repair shop. Refer to the Troubleshooting sec­tion at the front of this manual for information on symptoms of transmission problems.

Preliminary checks

1. Drive the vehicle to warm up the transmission to its normal operating temperature.

2. Check the fluid level as described in Chapter Tune-up and routine maintenance :

a) If the fluid level is unusually low, add enough fluid to bring the level within the area between the high and low marks on the dipstick (Fluid level checks ), then check for external leaks (see below).

b) If the fluid level is abnormally high, it might have been overfilled. Drain off the excess. On models with diesel engines, which use a main water-to-oil cooler in addition to an auxiliary air-to-oil cooler, the presence of engine coolant in the automatic transmission fluid could indi­cate a leak in the water-to-oil cooler, so check the drained fluid for coolant contamination. Only diesel engines use a water-to-oil cooler in addition to the external air-to-oil cooler.

c) If the fluid is foaming, drain it and refill the transmission, then check for coolant in the fluid or a high fluid level.

3. Check the engine idle speed. Note: If the engine is malfunctioning, do not proceed with the preliminary checks until it has been repaired and runs normally.

4. Inspect the shift cable (Shift cable – check, adjustment and replacement).
Make sure it’s properly adjusted and that it operates smoothly.

Fluid leak diagnosis

5. Most fluid leaks are usually easy to locate because they leave a visible stain and/ or wet spot. Most repairs are simply a matter of replacing a seal or gasket. If a leak is more difficult to find, the following procedure will help.

6. Identify the fluid. Make sure that it’s transmission fluid, not engine oil or brake fluid. One way to positively identify Automatic Transmission Fluid (ATF) is by its deep red color.

7. Try to pinpoint the source of the leak.

Drive the vehicle several miles, then park it over a large sheet of cardboard. After a min­ute or two, you should be able to locate the leak by determining the source of the fluid dripping onto the cardboard.

8. Make a careful visual inspection of the suspected component and the area immedi­ately around it. Pay particular attention to gas­ket mating surfaces. A flashlight and mirror are often helpful for finding leaks in areas that are hard to see.

9. If you still can’t find the leak, thoroughly clean the suspected area with a degreaser or solvent, then dry it off.

10. Drive the vehicle for several miles at normal operating temperature and varying speeds. After driving the vehicle, visually inspect the suspected component again.

11. Once you have located the leak, you must determine the source before you can repair it properly. For example, if you replace a pan gasket but the sealing flange is warped or bent, the new gasket won’t stop the leak. The flange must first be straightened.

12. Before attempting to repair a leak verify that the following conditions are corrected or they might cause another leak. Note: Some of the following conditions cannot be fixed without highly specialized tools and expertise. Such problems must be referred to a transmission repair shop or a dealer service department.

Gasket leaks

13. Inspect the pan periodically. Make sure that the bolts are tight, that no bolts are miss­ing, that the gasket is in good condition and that the pan is flat (dents in the pan might indi­cate damage to the valve body inside).

14. If the pan gasket is leaking, the fluid level or the fluid pressure might be too high, the vent might be plugged, the pan bolts might be too tight, the pan sealing flange might be warped, the sealing surface of the transmis­sion housing might be damaged, the gasket might be damaged or the transmission casting might be cracked or porous. If sealant instead of gasket material has been used to form a seal between the pan and the transmission housing, it may be the wrong type sealant.

Seal leaks

15. If a transmission seal is leaking, the fluid level or pressure might be too high, the vent might be plugged, the seal bore might be damaged, the seal itself might be damaged or incorrectly installed, the surface of the shaft protruding through the seal might be dam­aged or a loose bearing might be causing excessive shaft movement.

16. Make sure that the dipstick tube seal is in good condition and that the tube is correctly seated.

Case leaks

17. If the case itself appears to be leaking, the casting is porous. A porous casting must be repaired or replaced.

18. Make sure that the oil cooler hose fittings are tight and in good condition.

Fluid comes out vent pipe or fill tube

19. If this condition occurs, the transmission is overfilled, there is coolant in the fluid, the case is porous, the dipstick is incorrect, the vent is plugged or the drain-back holes are plugged.