Force Motor Circuit Check (LT. Truck): Notes

Fig 1: Force Motor Circuit Diagram (Lt. Truck)

Courtesy of GENERAL MOTORS CORP.

NOTE: This flow chart requires the use of a bidirectional (Tech 1) Scan tester.

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 appropriate line pressure or a given load, then regulates the pressure by applying a variable amperage to the force motor. The applied amperage varies from .1-1.1 amps.

NOTE: Test numbers refer to test numbers on diagnostic chart.

This test verifies an amperage difference of .16 amp or more, and tests the PCM/TCM's ability to control amperage to the force motor.
This test checks the force motor for internal shorts.