Transmission Control Systems: Description and Operation

Overdrive Light:

PURPOSE
A self-diagnosis function is built into the electrical control system. Warning is indicated by the overdrive OFF indicator light. Warning and diagnostic codes can be read only when the overdrive switch is ON. If OFF, the overdrive OFF light is lit continuously and will not blink.

OPERATION
If a malfunction occurs within the speed sensors (No.1 or 2) or solenoids (No.1 or 2), the overdrive OFF light will blink to warn the driver. A malfunction with the lock-up solenoid will set a code but will not cause the indicator to flash.

The diagnostic code can be read by the number of blinks of the overdrive OFF indicator light when terminals TE1 and E1 are connected.

The throttle position sensor or brake signal are not indicated, but inspection can be made by checking the voltage at terminal Tt of the check connector.

The signals to each gear can be checked by measuring the voltage at terminal Tt of the check connector while driving.

The diagnostic code (trouble code) is retained in memory by the ECU (of Engine & ECT ECU) and due to back-up voltage, is not canceled out when the engine is turned off. Consequently, after repair, it is necessary to turn the ignition switch off and remove the EFI fuse (15A) or disconnect the Engine & ECT ECU connector to cancel out the diagnostic (trouble) code.


NOTE:
^ Low battery voltage will cause false operation of the diagnosis system.
^ Use a voltmeter and ohmmeter that have an impedance of at least 10 K Ohms.