P063C

P063C-GENERATOR VOLTAGE SENSE LOW





For complete wiring diagrams refer to Diagrams/Electrical.


Theory of Operation

There are two communication lines between the ECM and alternator. Based on sensed battery voltage, the ECM commands the alternator to charge the batteries to a desired voltage. The max voltage the ECM will command the alternator to charge is 14.75 volts. The ECM then receives feedback from the alternator on the voltage level it is charging the batteries. The ECM will not light a MIL lamp for this fault.

- When Monitored:

Engine running.

- Set Condition:

Battery voltage exceeds charging voltage by more than a calibrated amount for a calibratable period of time.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. BATTERY TERMINALS DAMAGED, CORRODED, OR LOOSE CONNECTIONS

NOTE: Batteries must be fully charged and capable of passing a battery load test. The generator belt tension must be within specification. Inspect the vehicle for any aftermarket equipment that may exceed the maximum generator output.

Visually inspect the positive and negative connections at the battery. Visually inspect the battery negative connections at the engine block.

Are the connections free of corrosion and are they tight?

Yes

- Go To 2

No

- Clean and/or tighten the connections.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. (A804) GENERATOR SENSE CIRCUIT SHORTED TO GROUND

Turn the ignition off.

Disconnect the C1 ECM harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance between the (A804) Generator Sense circuit at the ECM harness connector and ground.

Is the resistance greater than 100 k Ohms?

Yes

- Go To 3

No

- Repair/replace harness for a short to ground.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

3. (A804) GENERATOR SENSE CIRCUIT OPEN

Measure the resistance of the (A804) Generator Sense circuit from the alternator harness connector to the ECM harness connector.

Is the resistance less than 10 ohms?

Yes

- Go To 4

No

- Repair/replace harness for an open circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. OPEN CIRCUIT BETWEEN GENERATOR AND AUXILIARY BATTERY

Disconnect the positive battery cables from both the primary and auxiliary battery.

Disconnect the harness from the auxiliary battery to the generator.

Measure the resistance in the harness that connects the auxiliary battery to the generator.

Is the resistance less than 10 ohms?

Yes

- Go To 5

No

- Repair/replace open circuit in wiring harness.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. GENERATOR

Measure the resistance between the generator output stud and the generator Sense circuit on the generator connector.

Is the resistance less than 10 ohms?

Yes

- Replace ECM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Replace generator.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test