Circuit Description
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The ECM uses the generator turn on signal circuit to control the load of the generator on the engine. A high-side driver in the ECM applies a voltage to the voltage regulator. When the ECM turns ON the high-side driver, the voltage regulator turns ON the field circuit. When the ECM turns OFF the high-side driver, the voltage regulator turns OFF the field circuit.
The ECM monitors the state of the generator turn on signal circuit. With engine running, ECM should detect a high generator turn on signal circuit or when the charging system malfunctions. If ECM detects a low generator turn on signal circuit, DTC P0621 will set. When DTC sets, ECM will send a class 2 serial data message to the IPC to illuminate the charge indicator.