PCM Controlled Generator Diagnosis

Circuit Description
The L-terminal circuit from the generator is a discrete into the PCM. The PCM supplies the ignition voltage to the generator lamp feed. This ignition voltage is pulled low by the generator once the ignition switch supplies ignition 1 voltage. The voltage stays low until the generator turns. When the generator is up and running, the PCM detects ignition voltage. Therefore, with no failures with the vehicle's charging system, the lamp terminal circuit will go low (0.0 volts) when the ignition switch is powered up and then goes to the ignition voltage after the engine is started.

The F-terminal circuit from the generator is a pulse width modulation (PWM) signal to the PCM. The PCM detects the PWM frequency by sampling the average voltage at the F-terminal of the generator. When the ignition switch supplies ignition 1 voltage, the generator goes to a predetermined duty cycle. When the generator is up and running, the generator regulator starts regulating and suppling the current. Therefore, with no failures with the vehicle's charging system, the field terminal circuit voltage will be at a low value and stay there until roughly 0.5 second after the engine idles. When the engine is idles, the voltage transitions to a higher value. When the charging system detects a fault (circuit shorted to ground), the Driver Information Center will display Charging System Fault.

Diagnostic Aids
A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, or open sense lead may cause a low battery charge. Refer to Starting and Charging for further information and generator diagnosis.

Use a scan tool in order to diagnosis the generator circuits. A scan tool displays Generator L-Terminal Inactive when there is a problem with the L-terminal circuit.

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
2. This step determines if a fault is present.
15. A poor connection at the generator causes no output.