Circuit Check - Force Motor

Force Motor Circuit:

Circuit Description:
The force motor is a PCM/TCM controlled device used to regulate transmission line pressure. The PCM/TCM looks at TPS voltage, engine rpm, and other inputs to determine the line pressure appropriate for a given load, then regulates the pressure by applying a variable amperage to the force motor. The applied amperage varies from .1 to 1.1 amps.

The PCM/TCM then monitors the amperage at the return line and if the return amperage varies more than .16 amp from the commanded amperage for a duration of at least 1 second, Code 73 is set. Once code 73 is set, the force motor is disabled and full line pressure will be applied until the next time the ignition key is cycled. Code 73 will remain stored but the force motor will resume normal function until the conditions for code 73 re-occur.

Force Motor Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks the ability of the PCM/TCM to command the force motor.

2. Checks for voltage at PCM/TCM.

3. Checks internal transmission harness and force motor for low resistance.

4. Checks for short to ground.

5. Checks internal transmission harness and force motor for high resistance.


Diagnostic Aids:
Check for poor connections at PCM/TCM and especially at transmission pass-thru connector.