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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open or High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Fuel Pump High Signal | P0231 | P023F | P0232 | P023F, P2635
Fuel Pump Low Signal | -- | P023F | -- | P023F, P2635

### Circuit/System Description

The engine control module (ECM) supplies voltage to the fuel pump flow control module (FPCM) when the ECM detects that the ignition is on. The voltage from the ECM to the FPCM remains active for two seconds, unless the engine is in crank or run. While this voltage is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel rail pressure.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Fuel 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

Control Module References for scan tool

### Circuit/System Verification

Ignition ON, command the fuel pump ON and OFF using the scan tool ECM output control. The fuel pump should turn on and off.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the G12 fuel pump.
2. Connect a test lamp between the control circuit terminal 2 and ground.
3. Ignition ON, command the G12 fuel pump ON and OFF using a scan tool ECM fuel pump output control. The test lamp should turn ON and OFF, as commanded.

⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K27 FPCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K27 FPCM.

4. Ignition OFF, connect a test lamp between the control circuit terminal 1 and the control circuit terminal 2.
5. Ignition ON, command the G12 fuel pump ON using a scan tool. The test lamp should illuminate.

⇒ | If the test lamp does not illuminate, test the control circuit terminal 2 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K27 FPCM.

6. If all circuits test normal, replace the fuel tank G12 fuel pump module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for FPCM replacement, setup, and programming