For 1990-2009 cars

The powertrain control module (PCM) controls the fuel pump motor by supplying ignition voltage to the fuel pump relay coil. The fuel pump runs continuously whenever the engine is running or runs for 2 seconds if the ignition is turned ON and the engine is not cranked. The PCM controls an internal driver which supplies the fuel pump relay coil direct ignition voltage whenever the fuel pump relay is commanded ON. The relay coil circuit is monitored for low and high voltage faults. DTC P0231 sets when the fuel pump relay is being commanded ON and the feedback voltage at the PCM is low.

### DTC Parameters

DTC P0231 will set if fuel pump relay feedback voltage is less than 2.5 volts with fuel pump relay commanded ON when:

• | The condition exists for longer than 0.5 seconds.

• | The ignition is ON.

DTC P0231 diagnostic runs continuously with ignition ON and fuel pump relay commanded ON.

DTC P0231 is a type D DTC.

### Diagnostic Aids

To locate an intermittent problem, use scan tool to command FUEL PUMP RELAY ON, while monitoring the FUEL PUMP REL. - LOW VOLT test. When a fault (short to ground or shorted solenoid) exists, the scan tool will display TEST FAIL.

The test will fail only when the device is being commanded ON and the voltage at the PCM is low. The test updates every 100 ms whenever the ignition is turned ON and the device is being commanded ON via the scan tool or PCM.

The PCM supplies voltage on circuit 465 when the fuel pump relay is commanded OFF. This voltage normally will not light a test light.

The fuel pump relay coil resistance is 75-105 ohms.