PCM Controlled Generator Diagnosis

Schematic:

CIRCUIT DESCRIPTION
The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the PCM. The. PCM applies ignition voltage to the generator L terminal circuit. A small amount of current flows from this circuit through the generator windings to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.

The PCM expects to detect low voltage on the L terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational. When the PCM detects a fault (circuit shorted to ground, or circuit shorted to a voltage), the battery lamp will illuminate.

DIAGNOSTIC AIDS

IMPORTANT:
^ Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
^ For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616-A. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Diagrams.

A generator fault, such as a shorted output diode, malfunctioning regulator, an open or shorted rotor, or an open sense lead may cause a low battery charge condition. Refer to A Diagnostic Starting Point Engine Electrical in Starting and Charing.

TEST DESCRIPTION

Diagnostic Chart:

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