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Home >> Chevy Truck >> 2012 >> Express 4500 V8-6.6L DSL Turbo >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P125A

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 0.5 s.

DTC P125B

The ECM detects high voltage on the supply voltage circuit of fuel pressure regulator 2 for greater than 0.1 s.

Action Taken When the DTC Sets

* DTC P125A is Type A DTC

* DTC P125B is Type B DTC

* The ECM commands the engine to operate in the Reduced Engine Power mode.

* The message center displays Engine Power Is Reduced.

Conditions for Clearing the DTC

* DTC P125A is Type A DTC

* DTC P125B is Type B DTC

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 1-2 Shift Solenoid (SS) Valve (M30)

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 Control Module References for scan tool information

Circuit/System Verification

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

* Fuel Press. Reg. 2 Ctrl. Ckt. Open Test Status

* Fuel Press. Reg. 2 Ctrl. Ckt. Short Gnd Test Status

* Fuel Press. Reg. 2 Ctrl. Ckt. Short Volt Test Status

* 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 Q45B fuel pressure regulator 2.

2. Connect a test lamp between the high control circuit terminal 1 and ground. Verify the test lamp does not illuminate.

• If the test lamp illuminates, test the high control 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 high control circuit terminal 1 and ground.

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

4. Ignition ON, verify that a test lamp does not illuminate between the low control circuit terminal 2 and ground.

• If the test lamp illuminates , test the low control circuit for a short to voltage. If the circuit tests normal, replace the K20 engine control module.

5. Ignition ON, verify a test lamp illuminates between the low control circuit terminal 2 and B+.

• If the test lamp does not illuminate, test the low control circuit for an open or high resistance. If the circuit tests normal, replace the K20 engine control module.

6. Ignition OFF, Observe that the test lamp flashes 2 times and remains OFF until the ECM is powered down.

• If the test lamp does not flash 2 times and turn OFF, test the low control circuit for a short to ground. If the circuit tests normal, replace the K20 engine control module.

7. If all circuits tests normal, replace the Q45B fuel pressure regulator 2.

Repair Instructions

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 Control Module References for ECM replacement, programming, and setup.

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