Circuit Description

The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when 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 by the rectifier bridge and is supplied to the electrical system at the battery terminal.

When the engine is running, the generator turn-on signal is sent to the generator from the engine control module (ECM)/powertrain control module (PCM), turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. 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 generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives B+ voltage that is Hot At All Times through the ECM/TCM fuse in the underhood junction block. This voltage is used by the regulator as the reference for system voltage control.

This vehicle uses Class II and controller area network (CAN) communications. The ECM/PCM are CAN and the body controller systems are Class II. The body control module (BCM) acts as the gateway between the different communication protocols. The ECM/PCM requests the battery lamp on the CAN communication line and then the BCM sends a request to the IPC for lamp illumination.

The ECM/PCM will request the battery lamp on under the following conditions:

• The ECM/PCM interprets the ignition is in the accessory position.
• The ECM/PCM is in the RUN power mode with the engine not running.
• Generator L terminal fault has been detected.
• Generator F terminal fault has been detected.

If the generator is not charging, it pulls the F terminal low causing an F terminal fault. Low voltage threshold is 10.5 volts for 4 minutes and engine at least 1,300 RPM. High threshold is 18 volts for 5 minutes.