PCM Controlled Generator Diagnosis

Diagnosis
Use the following diagnostic table to diagnose the generator L circuit.
Use the following scan tool parameter when diagnosing the PCM controlled generator.

Generator L Terminal - Range
Inactive/Active: The generator L terminal indicates whether the PCM is allowing the generator to operate. The PCM can disable the generator under certain conditions in order to ease starting. Active indicates that the PCM is allowing generator operation, while inactive indicates that the PCM is not allowing generator operation.

Circuit Description
The generator communicates to the Powertrain Control Module (PCM) over one line, the L or Lamp circuit. The PCM uses the L circuit to monitor faults in the charging system.

Diagnostic Aids
^ An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.
^ Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for the following items:
- Improper mating
- Broken locks
- Poor terminal to wiring connections
- Physical damage to the wiring harness

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
4. If the volts telltale lamp is not operating, either a short circuit or the IPC is malfunctioning. This determines whether the L circuit, generator or IPC is malfunctioning.
5. If the charging system is not functioning, system voltage cannot be maintained above 12 V. Turning off all accessories assures that the system voltage is not being drawn down by an accessory that normally draws a large current.
7. Refer to Instrument Panel Cluster (IPC) Microprocessor for replacement of the IPC.
8. If the lamp circuit is not shorted to ground, the volts telltale lamp will go OFF until the next key cycle when the test light is probed into terminal B. Be careful not to probe terminal C with the test light, this will turn off the volts telltale lamp whether or not the lamp circuit is shorted.
12. The PCM supplies a voltage to the generator. If voltage is available to the generator at this terminal, then the PCM and wiring are OK.
16. Program the replacement PCM. Perform the Crankshaft Position System Variation Learn Procedure. Refer to the latest Techline procedures for PCM programming.
17. If no malfunctions have been found at this point, refer to Diagnostic Aids for additional checks and information.