Circuit Description

The ECM uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to the high-side of the field winding in the generator. A Pulse Width-Modulated (PWM) high-side driver in the voltage regulator turns the field winding ON and OFF. The ECM uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads.

The ECM monitors the state of the generator field duty cycle signal circuit. When key is in the RUN position and engine is OFF, ECM should detect a duty cycle near zero percent. However, when engine is running, the duty cycle should be 5-100 percent. The ECM monitors the PWM signal, if ECM detects an out-of-range PWM signal, DTC P0622 will set. When DTC sets, ECM will send a Class 2 serial data message to the IPC to illuminate the charge indicator.