P125A

DTC P125A or P125B

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P125A
- Fuel Pressure Regulator 2 High Control Circuit Low Voltage

DTC P125B
- Fuel Pressure Regulator 2 High Control Circuit High Voltage

Diagnostic Fault Information





Typical Scan Tool Data










Circuit/System Description

The engine control module (ECM) controls the fuel rail pressure by controlling fuel pressure regulator 1 and fuel pressure regulator 2 simultaneously to achieve the desired fuel rail pressure. Fuel pressure regulator 2 is located on the front of the left hand side fuel rail and is used to control the amount of fuel that is bypassed to the fuel return system. Fuel pressure regulator 2 also allows fuel pressure leak down when the engine is OFF.

Conditions for Running the DTC

* Engine speed is greater than 600 RPM.
* Battery voltage is greater than 11 V.

Conditions for Setting the DTC

DTC P125A

The ECM detects low voltage on the supply voltage circuit of fuel pressure regulator 2 for greater than 1 s.

DTC P125B

The ECM detects high voltage on the supply voltage circuit of fuel pressure regulator 2 for greater than 1 s.

Action Taken When the DTC Sets

* DTC P125A and P125B are Type A DTCs
* The ECM commands the engine to operate in the Reduced Engine Power mode.
* The message center displays Reduced Engine Power.

Conditions for Clearing the DTC

DTC P125A and P125B are Type A DTCs

Diagnostic Aids

* A failure in the fuel pressure regulator 2 system could cause a crank no start condition.
* Intermittent or poor connections may cause this DTC to set.
* If the fuel system pressure is actually too high, a fuel knock condition may exist.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Fuel System Description (Fuel System Description)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Engine running, observe the following control circuit parameters with a scan tool:

* Fuel Press. Reg. 2 High Ctrl. Ckt. Short Gnd Test Status
* Fuel Press. Reg. 2 High Ctrl. Ckt. Volts Test Status
Each parameter should display OK or Not Run.

2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the fuel pressure regulator 2.
2. Connect a test lamp between the Fuel Rail Pressure Solenoid Supply Voltage circuit terminal A and ground. Verify the test lamp does not illuminate.

• If the test lamp illuminates, test the Fuel Rail Pressure Solenoid Supply Voltage circuit for a short to B+. If the circuit tests normal, replace the K20 engine control module.

3. Ignition ON, verify a test lamp illuminates between the Fuel Rail Pressure Solenoid Supply Voltage circuit terminal A and ground.

• If the test lamp does not illuminate, test the Fuel Rail Pressure Solenoid Supply Voltage circuit for an open, high resistance or short to ground. If the circuit tests normal, replace the K20 engine control module.

4. If all circuits test normal, replace the Q45B fuel pressure regulator 2.

Repair Instructions

Note: During code clearing, the ECM must be powered down. Power down is achieved by turning off the ignition key and waiting for loss of communication, indicating power down. The time to power down may vary from vehicle to vehicle. After power down is achieved, turn the ignition key to the ON position and clear the trouble code using the scan tool clear code function and power down ECM. Repeat power down if the trouble code does not clear on first attempt.

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Fuel Pressure Relief Valve Replacement (Service and Repair)
* Perform the scan tool Diesel Particulate Filter (DPF) Regeneration Enable (Diesel Particulate Filter (DPF) Regeneration Enable) procedure if the scan tool DPF Soot Mass is less than 30 g. If the scan tool DPF Soot Mass is 30 g or greater, perform the Diesel Particulate Filter (DPF) Service Regeneration (Diesel Particulate Filter (DPF) Service Regeneration) procedure.
* Control Module References (Programming and Relearning) for ECM replacement, programming, and setup.