Circuit Description

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

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.