AT/CVT Malfunction Diagnosis - General Information

Automatic transmission (AT) failures most often occur due to one of the following five causes: reduced engine torque output efficiency, incorrect adjustments, hydraulic system faults, mechanical damage, or failure of the powertrain control module (PCM) or its signal circuit. Fault diagnosis must always begin with the simplest checks: evaluate the ATF level and condition (refer to Section Maintenance and Routine Service), check the adjustment of the shift control cable and the transmission range switch. Next, carry out road tests of the vehicle to determine the effectiveness of the corrections made. If the problem cannot be corrected, drive the vehicle to a service station for more detailed diagnosis using special equipment. A description of some of the AT failure symptoms is given in the section on diagnosing faults of vehicle units and systems at the beginning of this Manual.

Preliminary Checks
PROCEDURE

1. Warm up the transmission to normal operating temperature during a short drive.
2. Check the ATF level (refer to Section Maintenance and Routine Service):

a) If the fluid level is clearly low, correct it by adding the required amount of fresh ATF. Verify the correct level using the dipstick, then check the transmission for signs of external leaks (see below);
b) If the level is too high, drain the excess ATF, then check it for traces of coolant, which indicate a leak in the internal partitions of the radiator separating its heat exchanger from the side ATF tanks (refer to Section Cooling and Heating Systems);
c) If the ATF is foamy, drain the transmission and refill it with fresh fluid, and check the drained fluid for traces of coolant.

3. Check the engine idle speed. Note: If the engine is not in good condition, do not begin preliminary transmission checks until the necessary corrections have been made.
4. Check the free movement of the throttle control cable (refer to Section Fuel and Exhaust Systems).
5. Check the shift control cable linkage (refer to Section Removal and Installation of the Gear Shift Lever/Selector), make sure it is correctly adjusted and moves freely.