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
--- | --- | --- | ---
Fuel Pump Relay Control | P0628 | P0627 | P0629

### Circuit/System Description

The engine control module (ECM) supplies voltage to the fuel pump control module when the ECM detects that the ignition is ON. The voltage signal from the ECM to the FPCM remains active for 2 seconds, unless the engine is in Crank or Run. While this signal is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel pump module in order to maintain the desired fuel pressure.

### Conditions for Running the DTC

#### P0627 and P0629

• | The ignition voltage is between 10-18.1 volts.

• | The ECM has commanded the fuel pump OFF.

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

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

#### P0628

• | The ignition voltage is between 10-18.1 volts.

• | The ECM has commanded the fuel pump ON.

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

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

### Conditions for Setting the DTC

#### P0627

The ECM detects the fuel pump relay control circuit is open.

#### 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 shorted to voltage.

The DTCs set when the above conditions are met for more than 4 seconds or a cumulative of 50 seconds.

### Action Taken When the DTC Sets

DTCs P0627, P0628, and P0629 are Type C DTCs.

### Conditions for Clearing the DTC

DTCs P0627, P0628, and P0629 are Type C 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 Testing

Note: Repair all U-codes before performing this diagnostic.

1. Ignition OFF, disconnect the harness connector at the K27 FPCM.
2. Install a test lamp between the fuel pump control circuit terminal 13 and ground. Verify the test lamp turns ON and OFF as the ignition is turned ON.

⇒ | If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

3. Ignition ON, verify that a test lamp does not stay illuminated between the fuel pump control circuit terminal 13 and ground.

⇒ | If the test lamp stays illuminated, test the control circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

4. If all circuits test normal, test or replace the K27 FPCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM or FPCM replacement, setup, and programming