Circuit Diagnosis - Fuel Pump

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
When the ignition switch is turned ON, the VCM turns ON the in-tank fuel pump. The in-tank fuel pump remains ON as long as the engine is cranking or running and the VCM is receiving the distributor reference pulses. If there are no reference pulses, the VCM shuts off the fuel pump within 2 seconds after the ignition ON or the engine stops.
Should the fuel pump relay or the 12 volt relay drive from the VCM fail, the fuel pump receives a supply current through the oil pressure switch backup circuit. The fuel pump test terminal is located in the driver's side of the engine compartment. When the engine is stopped, applying the battery voltage to the test terminal can turn on the fuel pump.

DIAGNOSTIC AIDS
If no trouble is found in the fuel pump circuit or the ignition system and the cause of an Engine Cranks But Will Not Run has not been found, check for the following conditions:
^ Fouled spark plugs.
^ An EGR valve stuck open.
^ Low fuel pressure. Refer to Fuel System Diagnosis. System Diagnosis - EGR
^ Water or foreign material in the fuel system.
^ A grounded Ignition Control (IC) signal circuit may cause a No Start or a Start then Stall condition.
^ Basic engine problem.
The VCM has integrated IC circuits that are fault protected; therefore, if a circuit has failed, the integrated IC may not be damaged. If that is the case, the IC will keep the circuit open until the fault in the circuit has been corrected.
When the fault has been corrected, reinstall the VCM and check the circuit. Replace the VCM only if the circuit is still inoperative.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step checks for the correct operation of the fuel pump system. When the ignition is turned ON, the fuel pump should operate for about 2 seconds and then turn OFF. if no ignition reference pulses are detected by the VCM.
3. This step checks the operation of the fuel pump by applying a fused 12 volts directly to the fuel pump. At this point, the problem is isolated as a pump or a control circuit problem.
4. This step will determine if the VCM is able to control the fuel pump relay.
5. This step will detect a problem in the Fuel Pump Relay control circuit.
7. This step checks for battery voltage to the Fuel Pump Relay. No voltage could be the result of an open battery circuit or a blown VCM B fuse. If the VCM B fuse is blown, the scan tool may not communicate with the vehicle.
8. The oil pressure switch serves as a backup for the fuel pump relay in order to help prevent a No Start situation. If the fuel pump relay was found to be inoperative, test the oil pressure switch circuit in order to determine why the switch did not operate the fuel pump.