Theory Of Operation

The Powertrain Control Module (PCM) uses the Generator field duty cycle signal circuit or F-terminal circuit, to monitor the duty cycle of the generator. The Generator field duty cycle signal circuit connects to high side of the field windings in the Generator. A Pulse Width Modulated (PWM) high side driver in the voltage regulator turns the field windings ON and OFF. The PCM uses the PWM signal input to determine the Generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads. The PCM monitors the status of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-95 percent.