Fuel Pump Electrical Circuit Diagnosis

Diagnostic Chart 1 Of 3:

Diagnostic Chart 2 Of 3:

Diagnostic Chart 3 Of 3:

Relay Cavity Identification Table:

Schematic:

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 across terminal 2 is 79-95 ohms at 20°C (68°F). The resistance across terminal 3 and across terminal 4 is infinite.
^ The fuel pump relay electrical contacts may be pitted or sticking. If wiggling or tapping gently on the fuel pump relay causes a change in the relay's operation, replace the fuel pump relay.
^ The temperature may affect the performance of the fuel pump relay. Check the fuel pump relay after sitting outside over night and after running the engine 30 minutes.

The fuel pump electrical resistance is 0.8-1.5 ohms at 20°C (68°F).

A fault in the fuel pump relay circuit may cause an intermittent malfunction. Inspect the wiring harness and the components for any of the following conditions:
^ Backed out terminals.
^ Incorrect mating of terminals.
^ Broken electrical connector locks.
^ Incorrectly formed terminals or damaged terminals.
^ Faulty terminal-to-wire connections.
^ Physical damage to the wiring harness.
^ A broken conductor inside the wire insulation.
^ Corrosion of electrical connections, of splices, or of 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 to save the applicable freeze frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The electronic copy can then be referred to for later reference.
2. This step checks if the fuel pump relay can operate the fuel pump. The PCM turns ON the fuel pump relay for 2 seconds when the ignition switch is cycled. Use an assistant in order to operate the ignition switch while you listen for fuel pump operation.
5. This step checks the control circuit of the fuel pump relay.
7. This step determines if the coil side of the fuel pump circuit is operating correctly.
10. This step checks for an electrical fault in the fuel tank or in the fuel pump wire harness.
17. This step determines whether the switched side of the fuel pump relay is always closed.