P020

Circuit Description

The fuel pump receives power from CKT 120 through either the fuel pump relay or oil pressure switch. The PCM energizes the fuel pump relay for 2 seconds at key on to provide fuel pressure for starting. After the 2 second fuel pump prime, the PCM will not power the fuel pump relay until 4X reference pulses are received indicating that the engine is turning (crank or run). The oil pressure switch is provided as a 'backup' to the fuel pump relay. A vehicle with fuel pump relay inoperative will crank until oil pressure builds (oil telltale or message off) then start and run as the pressure switch closes energizing the fuel pump. The PCM monitors voltage on the fuel pump power CKT 120 to detect fuel pump voltage supply faults. Code P020 is set when the PCM sees the fuel pump not energized (2 volts or less on the feedback) with the engine cranking or running. Since the the oil pressure switch closes when oil pressure increases after crank, this code will most likely set only during crank.

Test Condition(s)

RPM 24 or greater.

Failure Condition(s)

Fuel pump feedback 2 volts or less for 1.3 second.

Action Taken

PCM turns 'ON' the 'SERVICE VEHICLE SOON' message.

Notes on Fault Tree

1. Checking for engine to start. If it does, fuel pump relay operates correctly. Either fault is no longer present or CKT 120 to PCM is open. If it does not, fuel pump relay or circuits are at fault.
2. Checking if CKT 120 is open or if no fault is present.
3. Checking for an open in CKT 239 from fuse to fuel pump relay pin '5'.
4. Checking for an open in CKT 803 from S119 to fuel pump relay pin '2'.
5. Checking if fuel pump will run to isolate a fuel pump control problem from a fuel pump problem.
6. If greater than or equal to 10 volts is measured, then all fuel pump relay circuitry is OK. Fault is with fuel pump relay.
7. Checking for an open in CKT 120 from fuel pump relay to the fuel pump.
8. Checking for proper control of fuel pump relay by the PCM.
9. Checking for an open in CKT 804 fuel pump ground.
10. Checking CKT 239 for a short to ground.
11. Isolating where CKT 120 is shorted to ground.
12. Checking CKT 120 for a short to ground between oil pressure switch and PCM.
13. Checking fuel pump harness for a short to ground. If harness OK, short to ground must be in CKT 120 from fuel pump relay pin '3'.