P125B

P125B-POWER ENABLE CONTROL CIRCUIT HIGH





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

Theory of Operation

The Smart Power Relay supplies 12-volts to the Mass Airflow Sensor, the EGR Airflow Control Valve and the Variable Geometry Turbocharger. The Smart Power Relay Driver circuit is a low side driver controlled by the ECM. The Smart Power Relay is powered up at key on, and remains powered until just after key off. The power supply to the Smart Power Relay is wired directly from the TIPM. The ECM will light the MIL lamp and disable regeneration mode immediately after this diagnostic runs and fails. During this time there will likely also be voltage supply faults for the Mass Airflow Sensor, the EGR Airflow Control Valve and the Variable Geometry Turbocharger. The ECM will turn off the MIL lamp once the diagnostic runs and passes in four consecutive drive cycles.

- When Monitored:
Key on, Smart Power Relay commanded off.

- Set Condition:
The Smart Power Relay is commanded off by the ECM, and feedback voltage is reading low.





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

1. OTHER DTC'S
1. Ignition on, engine not running.
2. With the scan tool, read DTC's.

Is P125B active?

Yes

- Go To 2

No

- Refer to the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test

2. (A118) SMART POWER RELAY VOLTAGE SUPPLY
1. Remove the Smart Power Relay.

NOTE: Check connectors - Clean/repair as necessary.

2. Measure the voltage on the (A118) Smart Power Relay Voltage supply circuit at terminal #1 of the Smart Power Relay connector.

Does the voltage read battery voltage?

Yes

- Go To 3

No

- Repair the open in the (A118) Smart Power Relay Voltage supply circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

3. (K348) SMART POWER RELAY DRIVER CIRCUIT OPEN




1. Turn the Ignition off.
2. Remove the Smart Power Relay.
3. Disconnect the ECM C2 harness connector.

NOTE: Check connectors - Clean/repair as necessary.

4. Measure the resistance of (K348) Smart Power Relay Control circuit between terminal #5 of the Smart Power Relay connector and the ECM C2 harness connector.

Is the resistance below 10.0 ohms?

Yes

- Go To 4

No

- Repair the open (K348) Smart Power Relay Driver circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

4. (K348) SMART POWER RELAY CONTROL CIRCUIT SHORTED TO GROUND




1. Measure the resistance between ground and the (K348) Smart Power Relay Control circuit at terminal #5 of the Smart Power Relay connector.

Is the resistance below 10k ohms?

Yes

- Repair the short to ground in the (K348) Smart Power Relay Control circuit.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

No

- Go To 5

5. ECM
1. Replace the Smart Power Relay.
2. Turn the ignition on.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 30 seconds.
5. Turn the ignition on.
6. With the scan tool, read DTCs.

Did the DTC reset?

Yes

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

No

- Repair complete.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test