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 Descriptor

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 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 ECM 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 ECM turns OFF the fuel pump. The fuel pump relay control circuit is equipped with a feedback circuit that is pulled up to voltage 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 greater than 1 second.

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

### Conditions for Setting the DTC

#### 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.

#### DTC 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.

#### DTC 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, 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

#### 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 an audible click.
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 are captured in the Freeze Frame/Failure Records Data List.

### Circuit/System Testing

1. Ignition OFF, disconnect the fuel pump relay.
2. Test for less than 5 Ω between the ground circuit terminal 85 and ground.

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

3. Connect a test lamp between the control circuit terminal 86 and ground.
4. 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.

5. 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.

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

### Component Testing

1. Measure for 70-110 Ω between terminals 85 and 86 of the fuel pump relay.

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

2. Measure for infinite resistance between the following terminals of the fuel pump relay:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

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

3. Connect a 15 A fused jumper wire from B+ to relay terminal 86. Connect a jumper wire from ground to relay terminal 85. Test for less than 2 Ω between terminal 30 and 87 of the relay.

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

### Repair Instructions

Perform the Diagnostic Repair Verification .

• | Relay Replacement

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