Circuit Description

The powertrain control module (PCM)/engine control module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the PCM/ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. When the PCM/ECM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the PCM/ECM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.

The PCM/ECM monitors the state of the generator turn on signal circuit. The PCM/ECM should detect a low generator turn on signal circuit voltage when the key is ON and the engine is OFF or when the charging system malfunctions. With the engine running, the PCM/ECM should detect a high generator turn on signal circuit. The PCM/ECM performs key ON and RUN tests to determine the status of the generator turn on signal circuit. During the key ON test, if the PCM/ECM detects a high generator turn on signal circuit voltage, DTC P0621 will set. DTC P0621 will also set if, during the RUN test, the PCM/ECM detects a low generator turn on signal circuit. When the DTC sets, the PCM/ECM will send a serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator.