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 Side | ¹ | ² | -- | --
Fuel Pump Supply Voltage | ¹ | ² | ³ | --
Fuel Pump Relay Control | P0628 | P0629 | P0629 | --
Fuel Pump Relay Ground | -- | -- | -- | --
Fuel Pump Ground | -- | ² | -- | --
¹ Open fuel pump fuse, cranks, no start ² Cranks, no start ³ Fuel pump operates continuously, discharges battery

### 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

• | The ignition is ON.

• | The engine is running.

• | The fuel pump is running.

• | The ignition voltage is more than 9 volts.

• | These DTCs run continuously when the above conditions are met.

### Conditions for Setting the DTC

#### 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 open or shorted to voltage.

The DTCs set when the above conditions are met for 2.6 seconds.

### Action Taken When the DTC Sets

DTCs P0628 and P0629 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0628 and P0629 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Component Connector End Views

• | Inline Harness Connector End Views

#### 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 43244 Relay Puller Pliers

### Circuit/System Verification

1. Ignition ON, command the fuel pump relay ON and OFF with a scan tool. Listen/feel for relay to click and for fuel pump to turn ON and OFF.
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. Test for less than 5 ohms between the ground circuit and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit and the ground circuit.
4. Command the fuel pump relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

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

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

5. 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. Test for less than 2 ohms between terminals 30 and 87A.

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

5. 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 after completing the diagnostic procedure.

• | Relay Replacement

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