Fuel Pump Electrical Circuit Diagnosis

Schematic:

CIRCUIT DESCRIPTION
When the ignition switch is turned ON, the Powertrain Control Module (PCM) turns ON the in-tank fuel pump. It will remain ON as long as the PCM is receiving ignition reference pulses from the Ignition Control Module (ICM). If there are no reference pulses, the PCM will shut OFF the fuel pump about 2-3 seconds after the ignition is turned ON, about 10 seconds after the reference pulses stop.

The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. A fuel pressure regulator, attached to the fuel rail assembly, keeps the fuel available to the fuel injectors at a regulated pressure. The unused fuel is returned to the fuel tank by a separate fuel return pipe.

Improper fuel system pressure will result in one or all of the following symptoms:
^ Cranks but will not run
^ DTC P0171
^ DTC P0172
^ DTCP1171
^ DTC P0300
^ Cuts out, may feel like an ignition problem
^ Poor fuel economy, loss of power
^ Hesitation

DIAGNOSTIC AIDS
Intermittent concerns may be caused by one of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Inspect for a poor connection or a damaged harness. Inspect the PCM harness and connectors for the following conditions:
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Poor terminal to wire connections
^ Damaged harnesses

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

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 Power Control Module 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.
12. It may be necessary to lower the fuel tank to gain access to the fuel pump connector.
13. 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.
15. Use the same amperage fuse. Using a larger one may cause damage to the circuit and a smaller one may open to soon.
26. The replacement PCM must be programmed and the Crankshaft position System Variation Learn procedure must be performed.