Fuel Pump Electrical Circuit Diagnosis

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Schematic:

CIRCUIT DESCRIPTION
When the ignition switch is turned on, the Powertrain Control Module (PCM)turns on the in-tank fuel pump. The pump will remain on as long as the PCM is receiving ignition reference pulses from the electronic Ignition Control Module (ICM). If the PCM does not receive reference pulses, the PCM will shut off the fuel pump 2-3 seconds after the ignition is turned on, or about 10 seconds after the reference pulses stop.

The fuel pump delivers fuel to the fuel rail and the fuel injectors, then to the fuel pressure regulator where the pressure is controlled to the following pressure:

358-405 kPa (52-58 psi) with no manifold vacuum
OR
290-379 kPa (42-55 psi) with the engine at idle

Excess fuel is then returned to the fuel tank.

Improper fuel system pressure will result in one or all of the following symptoms:
^ The engine cranks but will not run
^ DTC P0171 set
^ DTC P0172 set
^ DTC P1171 set
^ DTC P0300 set
^ The engine cuts out
^ Reduced fuel economy and a loss of power
^ Engine hesitation

DIAGNOSTIC AIDS
An intermittent may be caused by the following conditions:
^ A faulty connection
^ A rubbed-through wire insulation
^ A broken wire inside the insulation
^ A damaged harness

Inspect the PCM harness and the connectors for the following items:
^ Any incorrectly mated electrical connectors
^ Any broken locks
^ Any improperly formed terminals or damaged terminals
^ Any faulty terminal-to-wire connections
^ Any damaged harnesses

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Command both the ON and OFF states. Repeat the commands as necessary.
3. This step determines if the condition is located on the coil side or the switch side of the circuit.
4. This step verifies that the PCM is providing voltage to the fuel pump relay.
5. This step tests for an open in the ground circuit to the fuel pump relay.
6. This step determines if a voltage is constantly being applied to the fuel pump relay.
15. Use the same amp fuse the circuit is protected with.
20. This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.
28. The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.