P2503

P2503-CHARGING SYSTEM OUTPUT 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-volt. 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:

The battery voltage exceeds target voltage by more than a calibrated value.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. ACTIVE DTC

With the scan tool, read DTCs.

Is DTC P065A active?

Yes

- Go To 2

No

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

2. GENERATOR

Disconnect the Generator field harness connector.


NOTE: Check connectors - Clean/repair as necessary.

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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

3. (K20) GEN FIELD CONTROL CIRCUIT SHORTED TO GROUND

Disconnect the ECM harness connectors.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance of the (K20) Generator Field Control circuit between the generator and battery negative.

Is the resistance greater than 100 ohms?

Yes

- Go To 4

No

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

4. ECM

Measure and record the voltage between battery positive circuit of the ECM harness connector and the battery negative circuits of the ECM harness connector.

Reconnect the ECM connectors.

Use the scan tool to measure and record battery voltage.

Compare the voltage reading from the voltmeter with that of the scan tool.

Are the readings within 3 volts of each other?

Yes

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

No

- Replace and program the ECM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test