With 4L80-E Automatic Transmission

Fuel Pump Relay Circuit Chart A-5:

Fuel Pump Relay Circuit:

Circuit Description:
When the ignition switch is turned "ON," the PCM will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the PCM is receiving distributor reference pulses. If there are no reference pulses, the PCM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.

A fuel module is used on all light duty vehicles over 8500 GVW, except 4.3L, to insure a rapid hot restart during a high ambient air temperature conditions. It is designed to over-ride the PCM two second pump operation and will run the fuel pump for twenty seconds at initial ignition "ON".

The pump will deliver fuel to the TBI unit where the system pressure is controlled to about 62 to 90 kPa (9 to 13 psi). Excess fuel is then returned to the fuel tank.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This procedure applies direct voltage to run the fuel pump. If the pump runs, it may be a fuel pump relay circuit problem which the following step will locate.

2. This step checks voltage from the battery and the ground circuit to the relay.

3. This test determines if there is voltage from the PCM, terminal "A", to terminal "D" on the relay connector.

4. This completes the fuel pump relay circuit but if this diagnosis was used because the engine would not run then oil pressure switch should also be diagnosed.

Diagnostic Aids:
An inoperative fuel module may be the cause of a hot stall/no start condition. Check for power and ground circuit to the fuel module and a complete circuit to the pump from terminal "A". If OK, and the pump does not run for the specified 20 seconds at initial ignition "ON", replace the fuel module.