GM Service Manual Online
For 1990-2009 cars only

The generator provides voltage in order to perform the following functions:

    • Operate the vehicle electrical system
    • Charge the vehicle battery

A magnetic field is created when current flows through the rotor. The magnetic field rotates while the rotor is driven by the engine. This rotation creates an alternating current (AC) voltage in the stator windings. The rectifier bridge converts the alternating current (AC) voltage to direct current (DC). The AC voltage is supplied to the electrical system at the battery terminal.

The generator's digital regulator uses digital techniques in order to supply the rotor current and control the output voltage. The rotor current is proportional to the width of the electrical pulses supplied by the digital regulator. When the ignition switch is in the RUN position, voltage is supplied to terminal B. This action turns ON the digital regulator. Narrow width pulses are supplied to the digital rotor. This action creates a weak magnetic field. When you start the engine, the digital regulator senses the generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the digital regulator varies the field current by controlling the pulse width. This action regulates the generator output voltage for the following conditions:

    • Correct battery charging
    • Correct electrical system operation

The powertrain control module (PCM) controls the CHARGE warning lamp using a solid state lamp driver. The lamp driver turns the lamp ON whenever the lamp driver detects the following conditions:

    • Undervoltage
    • Overvoltage
    • A stopped generator