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P0628




DTC P0627, P0628, or P0629

Diagnostic Instructions

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

DTC Descriptors
DTC P0627
- Fuel Pump Relay Control Circuit

DTC P0628
- Fuel Pump Relay Control Circuit Low Voltage

DTC P0629
- Fuel Pump Relay Control Circuit High Voltage

Diagnostic Fault Information





Circuit/System Description

The engine control module (ECM) provides ignition voltage to the coil side of the fuel pump relay whenever the engine is cranking or running. The control module enables the fuel pump relay as long as the engine is cranking or running, and ignition system reference pulses are received. If no ignition system reference pulses are received, the control module turns OFF the fuel pump. The fuel pump relay control circuit is equipped with a feedback circuit within the ECM. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

Conditions for Running the DTC

P0627 and P0629
* The engine speed is greater than 80 RPM.
* The ignition voltage is between 10-18.1 volts.
* The ECM has commanded the fuel pump relay OFF.
* The above conditions are met for greater than 1 second.
* The DTCs run continuously once the above conditions are met.

P0628
* The engine speed is greater than 80 RPM.
* The ignition voltage is between 10-18.1 volts.
* The ECM has commanded the fuel pump relay ON.
* The above conditions are met for greater than 1 second.
* The DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC

P0627

The ECM detects the fuel pump relay control circuit is open.

P0628

The ECM detects the fuel pump relay control circuit is shorted to ground.

P0629

The ECM detects the fuel pump relay control circuit is shorted to voltage.

The DTCs set when the above conditions are met for more than 4 seconds or a cumulative of 50 seconds.

Action Taken When the DTC Sets

DTCs P0627, P0628, and P0629 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0627, P0628, and P0629 are Type B DTCs.

Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

* Component Connector End Views (Connector Views)
* Inline Harness Connector End Views (Connector Views)

Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

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

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

J 43244 Relay Puller Pliers

Circuit/System Verification

Important: An open or a short to voltage in the control circuit will cause both the Ckt. Open Test Status and the Ckt. Short Volts Test Status parameters to display Fault.


1. Ignition ON, command the fuel pump relay ON and OFF with a scan tool while observing the following control circuit status parameters:

* Fuel pump relay Ckt. Short Gnd Test Status
* Fuel pump relay Ckt. Open Test Status
* Fuel pump relay Ckt. Short Volts Test Status

2. Each parameter should toggle between OK and Not Run, or Not Run and OK.

Circuit/System Testing

1. Ignition OFF, disconnect the fuel pump relay using the J 43244 .
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. Connect a 15A fused jumper wire between the positive voltage terminal at the battery and the supply voltage circuit terminal 87 of the fuel pump. Verify the fuel pump is activated.

• If the fuel pump does not activate, test the supply voltage circuit of the fuel pump for a short to ground or an open/high resistance. If the circuit tests normal, replace the fuel pump module.

8. Ignition ON, connect a 15A fused jumper wire between the B+ circuit terminal 30 and the supply voltage circuit terminal 87 of the fuel pump. Verify the fuel pump is activated.

• If the fuel pump does not activate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and it's fuse is open, test or replace the relay.

9. 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 an open/high resistance.

10. If all circuits and the ECM test normal, test or replace the fuel pump relay.

Component Testing
Relay Test

1. Ignition OFF, disconnect the fuel pump relay.
2. Test for 70-110 ohms between terminals 85 and 86.

• If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87

• If not the specified value, replace the relay.

4. Install a 15A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

• If greater than the specified range, replace the relay.

Repair Instructions

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

* Fuel Pump Module Replacement (Service and Repair)
* 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 (Programming and Relearning) for ECM replacement, setup, and programming

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