Part 1 of 2

Fuel System Power Supply Circuit:

Chart A-5 (1 Of 2):

CIRCUIT DESCRIPTION:

When the ignition switch is turned "ON," the Powertrain Control Module (PCM) will energize the fuel pump relay which completes the circuit to the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running and the PCM is receiving "C3I" reference pulses. If there are no reference pulses, the PCM will de-energize the fuel pump relay within 2.0 seconds after key "ON" or the engine is stopped.

The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled. Excess fuel pressure is bypassed back to the fuel tank. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal located in the engine compartment.

Improper fuel system pressure may contribute to one or all of the following symptoms:

^ Cranks but won't run.
^ Code E044 or E045.
^ Cuts out, may feel like ignition problem.
^ Hesitation, loss of power or poor fuel economy.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. If the fuse is blown, a short to ground in CKTs 120, 839, or the fuel pump itself is the cause.

2. Determines if the fuel pump circuit is being controlled by the PCM. The PCM should energize the fuel pump relay. The engine is not cranking or running, so the PCM should de-energize the relay within 2.0 seconds after ignition is turned "ON."

3. Turns "ON" the fuel pump, if CKT 120 wiring is OK. If the pump runs, it is a basic fuel delivery problem.

4. This test will determine if a short to ground on CKT 120 caused the fuse to blow. To prevent a mis-diagnosis, be sure the fuel pump is disconnected before the test.

5. Checks for a short to ground in the fuel pump relay harness CKT 839.