Part 1 of 2

Chart A-5 Part 1 Of 2 (Standard Cluster):

Chart A-5 Wiring Diagram (Standard Cluster):

CIRCUIT DESCRIPTION:

When the ignition switch is turned "ON", the ECM will energize the fuel pump relay which turns "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving distributor reference pulses. If there are no reference pulses, the ECM will de-energize the fuel pump relay which will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.

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 44 or 45
^ 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 pump itself is the cause.

2. This step determines if the fuel pump circuit is being controlled by the ECM. The ECM should energize the fuel pump relay and turn the fuel pump "ON". If the engine is not cranking or running, the ECM should de-energize the relay and/or fuel pump within 2 seconds after the ignition is turned "ON".

3. Applying B+ to the pump prime connector turns "ON" the fuel pump. This validates CKT 120 wiring. If the pump runs, it is a basic fuel delivery problem.

4. This test will determine of 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.