For 1990-2009 cars

### Circuit Description

The fuel pump relay is located in the underhood fuse block (UHFB). The engine control module (ECM) controls the fuel pump motor by supplying a ground to the fuel pump relay coil whenever the engine is cranking or running. When the fuel pump relay is commanded OFF, circuit not grounded, the voltage level at the ECM should be high, ignition voltage. When the fuel pump relay is commanded ON, circuit grounded, the voltage level at the ECM should be low. The ECM fuel pump relay feedback circuit uses a pull-up voltage, 2.6-4.6 volts, which allows the ECM to individually differentiate between an open, short to ground, or short to voltage. During engine crank, the ECM will command the fuel pump relay OFF for a very short amount of time during which it will test for an open/low voltage condition. This test is only performed once during engine crank. DTC P0231 will set if the ECM detects lower than normal feedback voltage when the fuel pump relay is commanded OFF with the engine cranking.

### Conditions for Setting the DTC

DTC P0231 will set if the fuel pump relay feedback voltage is less than 2.6 volts during the 250 microsecond test phase when the fuel pump relay is commanded OFF when:

• | The condition exists for longer than 250 microseconds.

• | The engine is cranking.

• | The battery voltage is between 7.5-15 volts.

DTC P0231 diagnostic runs only once during engine crank when the above conditions have been met.

DTC P0231 is a type D DTC.

### Diagnostic Aids

Important: The ECM will only energize the fuel pump relay when the engine is cranking or running. If the ignition is turned ON and the engine is not cranking, the fuel pump will NOT run.

To locate an intermittent problem, use the scan tool to command the FUEL PUMP RELAY ON and OFF while wiggling circuit 497.

Fuel pump relay coil resistance is 70-115 ohms.