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 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 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 when the conditions above 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 greater than 4 seconds, or for a cumulative time of 30 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 greater than 4 seconds, or for a cumulative time of 30 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 greater than 4 seconds, or for a cumulative time of 30 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.

### Diagnostic Aids

• | When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the correct orientation in the fuse block. Test the mating electrical terminals for tightness.

• | If the condition is intermittent, move the related harnesses and connectors, with the engine operating, while monitoring the scan tool circuit test status parameters for the component. The circuit test status parameter changes from OK or Not Run to Fault if there is a condition with the circuit or a connection.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component 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

### Circuit/System Verification

1. Ignition ON, command the fuel pump relay ON and OFF with a scan tool. You should hear or feel a click from the fuel pump relay.
2. Attempt to start the engine. Observe the DTC information with a scan tool. DTC P0627, P0628, or P0629 should not set.
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. Connect a test lamp between the control circuit terminal 86 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 circuit/connections test normal, replace the ECM.

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

4. Ignition OFF, connect a test lamp between the fuel pump relay control circuit terminal 86 and the ground circuit terminal 85 of the fuel pump relay.
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 ground circuit of the fuel pump relay.

6. Ignition ON, test for 2-3 V on the control circuit terminal 86 of the fuel pump relay.

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

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

### Component Testing

1. Test for 135-185 Ω between terminals 85 and 86 of the fuel pump relay.

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

2. Measure the resistance between the terminals of the fuel pump relay listed below. The DMM should display O.L.

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

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

3. Connect a 15 A fused jumper wire from the positive terminal of the battery to relay terminal 86. Connect a jumper wire from the negative terminal of the battery to relay terminal 85. Test for less than 2 Ω between terminals 87 and 30 of the relay.

⇒ | 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 engine control module (ECM) replacement, setup, and programming