Part 1 of 2

Chart A-5 Fuel System Electrical Circuit (Part 1 Of 2):

Fuel System Schematic:

CIRCUIT DESCRIPTION
When the ignition switch is turned "ON," the Powertrain Control Module (PCM) will activate the fuel pump relay with a 12 volt supply and run the in-tank fuel pump. The fuel pump will operate as long as the engine is cranking or running and the PCM is receiving ignition reference pulses. If the PCM is not receiving a 7x reference within 2 seconds when ignition is "ON," the PCM will respond by de-energizing the fuel pump relay.

Should the fuel pump relay or the 12 volt relay drive from the PCM fail, the fuel pump will receive supply current through the oil pressure switch back-up circuit.

The fuel pump "test" terminal is located on the front of the relay center in the engine compartment. If the engine is "OFF," the pump can be turned "ON" by applying battery voltage to the "test" terminal.

Improper fuel system pressure will result in one of the following conditions:

^ Cranks but will not run.
^ Diagnostic Trouble Code (DTC) 44.
^ DTC 45.
^ DTC 55.
^ Cuts out, may feel like an ignition problem.
^ Poor fuel economy, loss of power.
^ Hesitation.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the fuse is open, a short to ground in CKTs 120, 839 or the fuel pump itself is the cause.
2. This step determines if the fuel pump circuit is being controlled by the PCM. The PCM should energize the fuel pump relay and turn the fuel pump "ON." If the engine is not cranking or running, the PCM should de-energize the relay and/or fuel pump within 2 seconds after the ignition is turne.
3. Applying B+ to the fuel pump test terminal turns "ON" the fuel pump. This validates CKT 120 wiring, relay contacts and fuel pump.
4. This test will determine if a short to ground on CKT 120 caused the fuse to open. To prevent a misdiagnosis, 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.