Chart A-5 Fuel Pump Circuit Diagnosis

Diagnostic Chart A-5 (Part 1 Of 2):

Diagnostic Chart A-5 (Part 2 Of 2):

Fuel Control Wiring 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 electronic Ignition Control Module (ICM).

If there are no reference pulses, the PCM will shut "OFF" the fuel pump about 2-3 seconds after key "ON," or about 10 seconds after reference pulses stop. If sufficient oil pressure is present to close the oil pressure switch, the fuel pump will remain "ON" during cranking without reference pulses.

The pump delivers fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to 283 - 324 kPa (41 - 47 psi) with no manifold vacuum, or, 214 - 303 kPa (31 - 44 psi) at idle (manifold vacuum 17"Hg - 20"Hg.) Excess fuel is directed back to the fuel tank.

The fuel pump "test" terminal is located in the engine compartment. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the "test" terminal.

NOTE: Improper fuel system pressure will result in one or all of the following symptoms:
^ Engine cranks but will not run.
^ DTC44.
^ DTC45.
^ DTC55.
^ Cuts out, may feel like an ignition problem.
^ Poor fuel economy, loss of power.
^ Hesitation.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
Part 1
1. If the fuse is blown, 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 turned "ON."
3. Applying B+ to the pump test connector 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 blow. 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.

Part 2
6. Checks for an open CKT 451.
7. Check for PCM control of the fuel pump relay through CKT 465.
8. The fuel pump control circuit includes an engine oil pressure switch with a separate set of normally open contacts. The switch closes at about 28 kPa (4 psi) of oil pressure and provides a second battery feed path to the fuel pump. If the relay fails, the pump will continue to run using the battery feed supplied by the closed oil pressure switch.

NOTE: A failed pump relay will result in extended engine crank time because of the time required to build enough oil pressure to close the oil pressure switch and turn "ON" the fuel pump. There may be instances when the relay has failed but the engine will not crank fast enough to build enough oil pressure to close the switch. This or a faulty oil pressure switch can result in "Engine Cranks But Will Not Run."

9. Checks the fuel pump and engine oil pressure switch to be sure it provides battery feed to the fuel pump should the fuel pump relay fail.