Fuel Pump: Testing and Inspection

Fuel Pump Electrical Circuit Diagnosis

Refer to Engine Controls Schematics Fuel Enable and Fuel Gauge and Fuel Pumps and Fuel Senders .

Circuit Description

When the ignition is turned ON, the powertrain control module (PCM) turns the in-tank fuel pump ON. The in-tank fuel pump remains ON as long as the engine is cranking or running and the PCM is receiving is reference pulses from the ignition system. If there are no reference pulses, the PCM will turn the fuel pump OFF within 2-3 seconds after the ignition is ON or the engine stops. The PCM will also turn ON the fuel pump for 2 seconds when the ignition is turned to the OFF position.

The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled at 379-427 kPa (55-62 psi). Excess fuel is returned to the fuel tank. When the engine is stopped, the fuel pump can be turned ON with a scan tool.

Improper fuel system pressure will result in one or more of the following symptoms:

* Crank but will not run
* Cuts out, may feel like an ignition problem
* Poor fuel economy
* Loss of power
* Hesitation
* DTCS

Diagnostic Aids

An inoperative fuel pump relay can result in long cranking times. If the fuel pump relay circuit checks out OK, refer to Fuel System Diagnosis Fuel System Diagnosis.

Excessive fuel may also cause long cranking times which is accompanied by the following conditions:

* A start that is not as fast as normal
* A puff of black smoke at the tailpipe

An improperly connected or faulty EVAP canister control valve can cause this problem. Disconnect the EVAP purge hose from the EVAP canister control valve in order to diagnose. Refer to Evaporative Emission Control System Diagnosis Evaporative Emission Control System Diagnosis.

One or more leaking fuel injectors may also extend the cranking time. Perform the fuel injector Test, in the Injector Balance Test Table. Refer to Sequential Multiport Fuel Injector Balance Test Sequential Multiport Fuel Injector Balance Test.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and stores the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.
3. If the no start condition was due to a open fuse, locate and repair any shorts that may have caused the fuse to open before replacement.
4. This step determines if the fuel pump circuit can be controlled by the PCM. The PCM should energize the fuel pump relay and turn the fuel pump ON when commanded by the scan tool. If the engine is not cranking or running, the PCM should de-energize the relay and turn OFF the fuel pump after 2 seconds.
5. Jumping the fuel pump feed terminal to the fuel pump relay ignition feed terminal verifies that the fuel pump relay ignition feed circuit, the fuel pump feed circuit, the fuel pump and fuel ground are all OK.
8. Inspect for an open ground circuit.
17. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.
18. This step checks the fuel pump ground circuit on the body side of the body harness only. If the fuel pump ground circuit is OK, then the fuel pump feed circuit or the fuel pump ground circuit in the fuel tank harness or the fuel pump itself is malfunctioning.
21. This test will determine if a short to ground on the fuel pump feed circuit caused the fuse to open. To prevent mis-diagnosis, be sure the fuel pump harness is disconnected before the test.