For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P0628: Fuel Pump Relay Control Circuit Low Voltage
DTC P0629: Fuel Pump Relay Control Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Battery Voltage - Relay Switch | * | ** | -- | --
Ignition 1 Voltage - Relay Coil | P0628 | P0628 | P0563 | --
Fuel Pump Supply Voltage | * | ** | *** | --
Fuel Pump Relay Control | P0628 | P0628 | P0629 | --
Fuel Pump Ground | -- | ** | -- | --
* The fuel pump fuse opens and the engine cranks but does not run. ** The engine cranks but does not run. *** The fuel pump operates continuously and the battery will discharge.

### Circuit/System Description

The engine control module (ECM) provides a ground to the coil side of the fuel pump relay. When the ignition switch is first turned ON, the ECM energizes the fuel pump relay, which applies power to the fuel pump. The ECM enables the fuel pump relay as long as the engine is cranking or running, and crankshaft reference pulses are received. If no crankshaft reference pulses are received, the ECM de-energizes the fuel pump relay after about 3 seconds.

### Conditions for Running the DTC

• | The ignition is ON or the engine is running.

• | The DTCs runs continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0628

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

#### P0629

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

### Action Taken When the DTC Sets

DTC P0628 and P0629 are Type C DTCs.

### Conditions for Clearing the DTC

DTC P0628 and P0629 are Type C DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

#### Special Tools

• | J 35616 GM-Approved Terminal Test Kit

• | J 43244 Relay Puller Pliers

### Circuit/System Verification

1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear an audible click for about 3-5 seconds.
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 fuel pump relay.
2. Ignition ON, verify that a test lamp illuminates between the relay coil supply circuit terminal 86 and ground.

⇒ | If the test lamp does not illuminate, repair the relay coil supply circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect a test lamp between the relay coil control circuit terminal 85 and the relay coil supply circuit terminal 86.
4. Ignition ON, command the fuel pump relay ON with a scan tool. The test lamp should turn ON for about 3-5 seconds and then turn OFF.

⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If circuit tests normal, replace the ECM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal, replace the ECM.

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

### Component Testing

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

⇒ | If not within the specified range, replace the fuel pump 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 fuel pump relay.

4. Install a 20A 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 relay terminal 30 and 87.

⇒ | If greater than the specified range, replace the fuel pump relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for ECM replacement, setup, and programming