Fuel Pump: Testing and Inspection

System 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. The fuel pump will operate and pressurize the fuel system when the fuel pump relay is energized. The PCM receives ignition system reference pulses when the engine is being cranked or when the engine is running. The PCM will continue to energize the fuel pump relay as long as the PCM receives ignition system reference pulses. The PCM will de-energize the fuel pump relay when ignition system reference pulses are no longer detected.
The fuel pump will deliver fuel to the fuel injectors in the fuel rail at a controlled pressure. The controlled pressure is 270-310 kPa (38.5-44 psi) when the fuel pump is energized and the engine not running. The controlled pressure is 200-240 kPa (28.5-34 psi) when the engine is idling at normal operating temperatures. The fuel pressure regulator maintains the correct fuel pressure at all times by returning excess fuel to the fuel tank.

Diagnostic Aids
Improper fuel system pressure can result in any of the following conditions:
^ The engine cranks but will not start.
^ The engine cuts out or stalls (may feel like an ignition malfunction).
^ A decrease in fuel economy and a decrease in power.
^ Hard starting

Check for water contamination of the fuel if the vehicle won't start in freezing weather. Ice can form in the fuel system and prevent the fuel from reaching the fuel injectors at the necessary fuel pressure and volume.Normal fuel pump electrical resistance is 0.8-1.5 ohms at 20°C (68°F).

An intermittent malfunction may be caused by a fault in the fuel pump 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.
^ A broken wire inside the insulation.
^ Corrosion of electrical connections, splices, or terminals.

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.
3. This step checks to see if fuel system pressure is within specifications with the ignition ON and the fuel pump running. The fuel pump may be operated with the scan tool Output Control feature when the fuel level is greater than 20 percent and no DTCs are set.
4. This step checks the fuel pressure after the fuel pump stops. Approximately one minute after the fuel pump stops fuel pressure should remain steady at 200 kPa (28.5 psi). The fuel pump may be operated with the scan tool Output Control feature when the fuel level is greater than 20 percent and no DTCs are set.
5. The vehicle should start and run. At this step adequate fuel pressure is available for the engine to operate. A vehicle that will not start may have inoperable injectors. Check the fuel injectors and the fuel injector circuitry. Refer to Fuel Injector Circuit Diagnosis.
6. This step checks for normal fuel pressure when the engine is running. Fuel pressure that is not within the specified value indicates a possible fault in the fuel pressure regulator.
8. This step checks for a faulty check valve in the fuel pump. The fuel pump may be operated with the scan tool Output Control feature when the fuel level is greater than 20 percent and no DTCs are set.
9. This step checks for a faulty check valve in the fuel pump. Blocking (pinching) the fuel feed hose between the fuel pressure gauge and the fuel pump, immediately after the fuel pump stops, traps the fuel pressure between the fuel pressure regulator and the blocked section. If fuel pressure now remains above the specified value, the fault is between the blocked section and the fuel tank. The fuel pump may be operated with the scan tool Output Control feature when the fuel level is greater than 20 percent and no DTCs are set.
12. This step checks for a faulty fuel pressure regulator. The fuel pump may be operated with the scan tool Output Control feature when the fuel level is greater than 20 percent and no DTCs are set.
13. Low fuel pressure or no fuel pressure may be caused by a fault in the fuel pump electrical circuit. Go to the Fuel Pump Relay Circuit Diagnosis in order to diagnose the fuel pump electrical circuit.
14. This step checks for additional conditions that can cause low fuel pressure other than a faulty fuel pump. Check for any restrictions or blockage in the fuel feed lines and hoses, including those inside the fuel tank. Check the fuel pump electrical circuit for excessive resistance. Proper fuel pump operation requires correct voltage and adequate current flow.
15. This step checks the operation of the fuel pressure regulator. The fuel pump may be operated with the scan tool Output Control feature when the fuel level is greater than 20 percent and no DTCs are set. Component Tests and General Diagnostics