P2503

P2503-CHARGING SYSTEM OUTPUT LOW





For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.

Theory of Operation

There are two communication lines between the Engine Control Module (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:
While the engine is running.

- Set Condition:
Battery voltage is less than 11.5 volts for more than eight seconds. Battery voltage must exceed 12 volts for more than five seconds for fault to become inactive.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. ACTIVE DTC
1. With the scan tool, read DTCs.

Is DTC P065A active?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

2. GENERATOR
1. Turn the ignition off.
2. Disconnect the Generator field harness connector.

NOTE: Check connectors - Clean/repair as necessary.

3. Measure the resistance between the generator field terminals at the generator.

Is the resistance between.5 and 15 Ohms?

Yes

- Go To 3

No

- Replace the generator.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. (K20) GEN FIELD CONTROL CIRCUIT SHORTED TO GROUND
1. Disconnect the ECM C1 harness connector.

NOTE: Check connectors - Clean/repair as necessary.

2. Measure the resistance between ground and the (K20) Generator Field Control circuit at the Generator field harness connector.

Is the resistance below 10k Ohms?

Yes

- Repair the short to ground in the (K20) Generator Field Control circuit shorted to ground.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 4

4. (K20) GEN FIELD CONTROL CIRCUIT OPEN
1. Measure the resistance between of the (K20) Generator Field Control circuit between the Generator field harness connector and the ECM C1 harness connector.

Is the resistance below 10.0 Ohms?

Yes

- Go To 5

No

- Repair the open or high resistance in the (K20) Generator Field Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

5. ENGINE CONTROL MODULE (ECM)
1. Measure and record the voltage between battery positive circuit of the ECM harness connector and the battery negative circuits of the ECM harness connector.
2. Reconnect the ECM connectors.
3. Use the scan tool to measure and record battery voltage.
4. Compare the voltage reading from the voltmeter with that of the scan tool.

Are the readings within 3.0 volts of each other?

Yes

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

No

- Replace and program the Engine Control Module (ECM).
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.