P125B

P125B-POWER ENABLE CONTROL CIRCUIT HIGH





For a complete wiring diagram Refer to Diagrams/Electrical.

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 for the Smart Power Relay. The Smart Power Relay Driver circuit is controlled by the ECM via a low side driver. 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 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.

- Set Condition:
The ECM detects the Smart Power Relay driver is on for more than a calibrated period of time.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview


Diagnostic Test


1. OTHER DTC'S
Ignition on, engine not running.
With the scan tool, read DTC's.
Is P125A active?

Yes


- Go To 2


No


- Refer to the INTERMITTENT CONDITION Symptom. Intermittent Condition



2. VOLTAGE SUPPLY TO SMART POWER RELAY
Measure the voltage between Smart Power Relay supply circuit and ground.
Is voltage equal to battery voltage?

Yes


- Go To 3


No


- Repair open circuit to Smart Power Relay supply.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test



3. (K348) SMART POWER RELAY DRIVER CIRCUIT OPEN
Turn the Ignition off.
Disconnect the Smart Power Relay harness connector.
Disconnect the (C2) ECM harness connector.

NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance between the Smart Power Relay harness connector Power Relay Driver circuit and the (C2) ECM harness connector Power Relay Driver circuit.
Is the resistance less than 10 ohms?

Yes


- Go To 4


No


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



4. ECM
Measure the resistance between the (K348) Smart Power Relay Driver circuit in the ECM harness connector and all other circuits in the ECM harness connector.
Is the resistance greater than 100k ohms?

Yes


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


No


- Repair complete.