PCM Controlled Generator Diagnosis

Diagnostic Chart:

Wiring Diagram:

DIAGNOSIS

Use the following diagnostic tables to diagnose the generator F and L circuit. Refer to Starting and Charging when diagnosing the remaining circuits.

CIRCUIT DESCRIPTION

The generator communicates to the Powertrain Control Module (PCM) over two lines, the L or Lamp circuit and the F or Field circuit. The PCM uses the L circuit to monitor faults in the charging system. The F circuit is used by the PCM to monitor the duty cycle or load of the generator. The PCM will adjust the idle speed according to the generator load.

DIAGNOSTIC AIDS

^ It CKT 23 is shorted to voltage, the volts telltale lamp will operate normally. However, the scan tool GEN F will display a generator duty cycle near 10 %. Check CKT 23 for a short to voltage. If OK, the generator may be faulty, refer to Starting and Charging when diagnosing the remaining circuits.

^ 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

Number(s) below refer to the step number(s) 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 fault 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 at fault. This determines whether the L circuit, generator or IPC is at fault.

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, Gauges and Warning Indicators for replacement of the IPC.

8. When the engine is not running, the generator duty cycle will be displayed above 5%. If the generator duty cycle reads 0%, then the field circuit is either open or shorted to ground.

9. 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.

14. 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.

20. Replacement PCM's must be reprogrammed. Refer to the latest Tech line information for programming procedures.

21. If no faults have been found at this point, refer to Diagnostic Aids for additional checks and information.