GM Service Manual Online
For 1990-2009 cars only

The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when the current flows through the rotor. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC voltage by the rectifier bridge, and is supplied to the electrical system at the battery terminal.

The generator's regulator uses digital techniques to supply the rotor current and thereby control the output voltage. The rotor current is proportional to the width of the electrical pulse supplied by the regulator. When the ignition switch is placed in the RUN position, voltage is supplied to terminal L, turning on the regulator. Narrow width pulses are supplied to the rotor creating a weak magnetic field. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The regulator sends an output to the powertrain control module which lights the charge Indicator via Serial Data if a malfunction is detected.