GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H2 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Charging System Description and Operation

Generator

The generator is non-serviceable. Service should only include tightening of mount components. If there is a diagnosed failure of the generator, it must be replaced as an assembly.

Regulator

The voltage regulator controls the field current of the rotor in order to limit system voltage. The regulator switches the current on and off at a rate of 400 cycles per second in order to perform the following functions:

    • Radio noise control
    • Obtain the correct average current needed for proper system voltage control

At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

Charging System Indicator

The IPC illuminates the charge indicator and the BATTERY NOT CHARGING message is displayed in the message center when the following occurs:

    • The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a serial data message from the PCM requesting illumination.
    • The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a serial data message from the body control module (BCM) indicating the system voltage.
    • The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
    • The ignition is on, with the engine off.

Circuit Description

Moving the ignition switch to the START position sends a 12 volt signal to the powertrain control module (PCM) Crank Request circuit. The PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag.