Fuel Pump Relay: Description and Operation

Fuel Pump Circuit:

PURPOSE
The PCM controls the fuel pump relay which operates the in-tank fuel pump.

OPERATION
Fuel pump relay #1 allows the fuel pump to be energized by the PCM. When the ignition is first turned "ON", the PCM energizes fuel pump relay #1 for two seconds. This allows the fuel pump to run for two seconds and build up fuel pressure for cranking. The PCM then waits for ignition reference pulses from the Ignition Control Module. Once the PCM sees reference pulses, the PCM energizes relay #1 to run the fuel pump.

As a backup system to the PCM and fuel pump relay #1, the fuel pump can also be turned on by the oil pressure sensor through fuel pump relay #2. If the PCM or fuel pump relay #1 is faulty and the engine is cranked, the oil pressure switch contacts of the sensor will close once oil pressure is built up and energize fuel pump relay #2, which then runs the fuel pump.


LOCATION
Both relays are located in the Battery compartment micro relay center which is behind the passenger seat.


DIAGNOSTIC NOTES
- The PCM will monitor the fuel pump circuit for proper operation and set the appropriate PCM code if necessary.

- The PCM monitors voltage on the fuel pump power CKT 120 to detect fuel pump voltage supply faults.

- A faulty fuel pump relay #1 will cause long cranking time and should set a trouble code. A faulty fuel pump relay #2 will only cause a "no start" condition if fuel pump relay #1 is also disabled.