Chart A-5 Fuel Pump Relay Circuit Diagnosis

Chart A-5.:

Fuel Pump Relay Circuit:

CIRCUIT DESCRIPTION
When the ignition switch is turned "ON," the Powertrain Control Module (PCM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the PCM is receiving low resolution reference pulses from the distributor ignition system.

If there are no reference pulses, the PCM will shut "OFF" the fuel pump about 2-3 seconds after key "ON," or when engine stops. When sufficient oil pressure is present to close the oil pressure switch, the fuel pump will remain "ON."

The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to 284-325 kPa (41-47 psi). Excess fuel is then returned to the fuel tank.

When the engine is stopped, the fuel pump can be turned "ON" by using the Tech 1 (or equivalent) Scanner. Improper fuel system pressure will result in one or all of the following symptoms:
^ Cranks but won't run.
^ DTC 44 and 64.
^ DTC 45 and 65.
^ Cuts out, may feel like ignition problem.
^ Poor fuel economy, loss of power.
^ Hesitation.
^ DTC 55.