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 Enable Circuit
DTC P0628: Fuel Pump Enable Circuit Low Voltage
DTC P0629: Fuel Pump Enable Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Fuel Pump Enable | P0628 | P0627 | P0629 | --

### Circuit/System Description

The engine control module (ECM) provides ignition voltage to the fuel pump flow control module (FPCM) whenever the engine is cranking or running. The control module enables the FPCM as long as the engine is cranking or running, and ignition system reference pulses are received. While this enable voltage is being received, the FPCM supplies a varying voltage to the in-tank fuel pump module in order to maintain the desired fuel line pressure.

### 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 enable circuit ON and OFF at least once during the ignition cycle.

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

### Conditions for Setting the DTC

#### P0627

The ECM detects the voltage on the fuel pump enable circuit is within a predetermined range when the enable circuit is commanded ON. The condition exists for greater than 4 seconds, or a cumulative of 30 seconds.

#### P0628

The ECM detects the fuel pump enable circuit voltage is less than 2.21 volts when the enable circuit is commanded OFF. The condition exists for greater than 4 seconds, or a cumulative of 30 seconds.

#### P0629

The ECM detects the fuel pump enable circuit voltage is greater than 2.74 volts when the enable circuit is commanded OFF. The condition exists for greater than 4 seconds, or a cumulative 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. Attempt to start the engine. Observe the DTC information with a scan tool. DTC P0627, P0628, or P0629 should not set.
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 control module (FPCM) harness connector.
2. Connect a test lamp between the enable circuit terminal 13 of the FPCM 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 for a short to ground or an open/high resistance on the enable circuit. If circuit/connections test normal, replace the ECM.

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

4. Ignition ON, test for 2-3 V on the enable circuit terminal 13 of the FPCM.

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

5. If all circuits/connections test normal, replace the FPCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Pump Flow Control Module Replacement

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