Circuit Description

PCM uses the "F" terminal circuit to monitor the duty cycle of the field circuit. The "F" terminal connects the he high side of the field winding in generator. A Pulse Width Modulated (PWM) high side driver in voltage regulator turns the field winding on and off. PCM uses PWM signal input to determine generator load on engine, allowing PCM to adjust idle speed to compensate for high electrical loads.

PCM monitors state of the "F" terminal circuit. When ignition is in RUN position, with engine off, PCM should detect a duty cycle near zero percent. PCM monitors the PWM signal using key on and run test. During this tests, if PCM detects an out of range PWM signal, DTC will set. When DTC sets, PCM will send a Class II serial data message to illuminate appropriate malfunction indicator light.