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 provide 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Battery Voltage - Relay Switch | 1 | 2 | -- | --
Fuel Pump Supply Voltage | 1 | 2 | 3 | --
Fuel Pump Relay Control | P0628 | P0627 | P0629 | --
Fuel Pump Relay Ground | -- | P0627 | -- | --

1. The fuel pump fuse opens and the engine cranks but does not run.
2. The engine cranks but does not run.
3. The fuel pump operates continuously and the battery will discharge.

### 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 that is pulled up to 2.5 volts 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 engine speed is greater than 80 RPM.

• | The ignition voltage is greater than 10-18 volts.

• | The ECM has commanded the fuel pump relay ON and OFF at least once during the ignition cycle.

• | The above conditions are met for less than 1 second.

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

### Conditions for Setting the DTC

#### P0627

The ECM detects the voltage on the fuel pump relay control circuit is within a predetermined range when the control circuit is commanded OFF. The condition exists for a cumulative of 50 seconds.

#### P0628

The ECM detects the fuel pump relay control circuit voltage is less than 2.21 volts when the control circuit is commanded OFF. The condition exists for a cumulative of 50 seconds.

#### P0629

The ECM detects the fuel pump relay control circuit voltage is greater than 2.74 volts when the control circuit is commanded ON. The condition exists for a cumulative of 50 seconds.

### Action Taken When the DTC Sets

DTCs P0627 and P0628 are Type C DTCs.

DTC P0629 is a Type B DTC.

### Conditions for Clearing the DTC

DTCs P0627 and P0628 are Type C DTCs.

DTC P0629 is a Type B DTC.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Description and Operation

Throttle Actuator Control (TAC) System Description

#### 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Ignition ON, command the Fuel Pump Relay ON and OFF with a scan tool. You should hear an audible click.

### Circuit/System Testing

1. Ignition OFF, disconnect the fuel pump relay.
2. Connect a test lamp between the control circuit of the fuel pump relay and ground.
3. Ignition ON, command the fuel pump ON and OFF with a scan tool. The test lamp should turn ON and OFF as commanded.

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

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

4. Ignition OFF, connect a test lamp between the fuel pump relay control circuit and the ground circuit.
5. Ignition ON, command the fuel pump ON and OFF with a scan tool. The test lamp should turn ON and OFF as commanded.

⇒ | If the test lamp does not turn ON when commanded, repair the open/high resistance in the ground circuit.

6. Ignition ON, test for 2-3 volts on the control circuit of the fuel pump relay.

⇒ | If the voltage is not within the specified range, replace the ECM.

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

### Component Testing

1. Measure for 110-150 ohms of resistance between terminals 1 and 2 of the fuel pump relay.

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

2. Measure for infinite resistance between the following terminals:

• | 3 and 2

• | 3 and 5

• | 3 and 1

• | 1 and 5

⇒ | If continuity is detected, replace the fuel pump relay.

3. Connect a 15A fused jumper wire from the positive terminal of the battery to relay terminal 1. Connect a jumper wire from the negative terminal of the battery to relay terminal 2. Measure for less than 2 ohms between terminal 3 and 5 of the relay.

⇒ | If more than the specified value, replace the fuel pump relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for engine control module replacement, setup, and programming