Fuel Pump Relay Circuit Diagnosis

Circuit Description
The powertrain control module (PCM) will energize the fuel pump relay for 2 seconds when the ignition switch is turned to the ON position. When the fuel pump relay is energized the fuel pump will operate and pressurize the fuel system. The fuel pump will continue to operate as long as the PCM is receiving ignition system reference pulses. The fuel pump will stop after 2 seconds if ignition system reference pulses are not detected.

Diagnostic Aids
Check for any of the following conditions:
^ Check the resistance of the fuel pump relay. The resistance across terminal 1 and terminal 2 is 79-95 ohms at 20°C (68°F). The resistance across terminal 3 and terminal 4 is infinite.
^ The fuel pump relay's electrical contacts may be pitted or sticking. Replace the fuel pump relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation.
^ The performance of the fuel pump relay may be affected by temperature. Check the fuel pump relay after sitting outside overnight and after running the engine 30 minutes.

Normal fuel pump electrical resistance is 0.1-1.5 ohms at 20°C (68°F).

An intermittent malfunction may be caused by a fault in the fuel pump relay electrical circuit. Inspect the wiring harness and components for any of the following conditions:
^ Backed out terminals.
^ Improper mating of terminals.
^ Broken electrical connector locks.
^ Improperly formed or damaged terminals.
^ Faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ Broken conductor inside the wire insulation.
^ Corrosion of electrical connections, splices, or terminals.

Use the relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks whether the fuel pump relay can operate the fuel pump. The PCM turns ON the fuel pump relay for 2 seconds when ever the ignition is cycled. Use a helper to operate the ignition switch while you listen for fuel pump operation or use a scan tool. The scan tool can be used to turn the fuel pump relay ON and OFF. The PCM will disable fuel pump relay control if any DTCs are set or if the fuel level is less than 20 percent.
3. This step checks the fuel pump relay control circuit.
8. This step checks for an electrical fault in the fuel tank or fuel pump wire harness.
19. The PCM will not turn ON the fuel pump relay while cranking the engine if there is no ignition reference pulses to the PCM. Check for a DTC P0335 and diagnose the DTC before replacing the PCM.