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P0628




DTC P0628 or P0629 (L96)

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 P0628
- Fuel Pump Enable Circuit Low Voltage

DTC P0629
- Fuel Pump Enable Circuit High Voltage

Diagnostic Fault Information





Circuit/System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The control module monitors the voltage on the fuel pump enable circuit. If the control module detects an incorrect voltage on the fuel pump enable circuit, a fuel pump enable circuit DTC sets.

Conditions for Running the DTC

* The engine speed is greater than 0 RPM.
* The ignition voltage is between 11-18 volts.
* The DTCs run continuously when the conditions above are met.

Conditions for Setting the DTC

* The control module detects that the commanded state of the driver and the actual state of the control circuit do not match.
* The above condition is met for a minimum of 2.5 seconds.

Action Taken When the DTC Sets

DTCs P0628 and P0629 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0628 and P0629 are Type B DTCs.

Reference Information
Schematic Reference

Engine Controls Schematics (except L96) ([1][2]Electrical Diagrams)Engine Controls Schematics (L96) ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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
Special Tools

J 43244 - Relay Puller Pliers

Circuit/System Verification

1. Attempt to start the engine. Observe the DTC information with a scan tool. DTC P0628 or P0629 should not set.
2. Ignition ON, command the fuel pump ON and OFF with a scan tool while observing the following control circuit status parameters:

* Fuel Pump Enable Circuit Low Voltage Test Status
* Fuel Pump Enable Circuit Open Test Status
* Fuel Pump Enable Circuit High Voltage Test Status
Each parameter should toggle between OK and Not Run or Not Run and OK.

3. 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 fuel pump relay.
2. Ignition ON, verify that a test lamp illuminates between the ground circuit terminal 85 and B+.

• If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance.

3. Verify that a test lamp does not illuminate between the ground circuit terminal 85 and the control circuit terminal 86.

• If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Remove the test lamp.
5. Command the fuel pump relay ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is OK.

• If not the specified value, test the fuel pump relay control circuit for a short to ground. If the circuit tests normal, replace the ECM.

6. Install a 3A fused jumper wire between the fuel pump relay control circuit terminal 86 and the ground circuit terminal 85. Command the fuel pump ON with a scan tool. Verify the scan tool fuel pump relay Ckt. Short Grnd Test Status parameter is Fault.

• If not the specified value, test the fuel pump relay control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

7. If all circuits test normal, test or replace the fuel pump relay.

Repair Instructions

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

* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Control Module References) for ECM replacement, setup, and programming

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