P020

DTC PO20: Part 1 Of 3:

DTC PO20: Part 2 Of 3:

DTC PO20: Part 3 Of 3:

Fuel Pump Circuit:

DESCRIPTION
The fuel pump receives power from CKT 120 through either fuel pump relay or the oil pressure switch. The Powertrain Control Module (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 distributor 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. Normal operating engine oil pressure will close the normally open switch contacts in the oil pressure switch providing a connection between CKTs 239 and 120. If a relay fault occurs, the engine will continue to run as the oil pressure switch powers the fuel pump. A vehicle with the relay inoperative will crank until oil pressure builds (oil telltale off) then start and run as the switch provides power to 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 (0 volt on the feedback) with the engine cranking or running. The code is designed to detect a fuel pump relay fault; relay not powering the fuel pump.

TEST CONDITIONS
RPM 24 or greater.

FAILURE CONDITIONS
Fuel pump feedback 2 volts or less for 1.3 seconds.

ACTION TAKEN
PCM turns "ON" the "SERVICE VEHICLE SOON" message.

NOTES ON FAULT TREE
(Part 1 of 3)
1. Checking for engine to start with fuel pump powered through fuel pump relay. If vehicle does not start, refer to diagnostic chart in accompanying image.

2. 0 volt With engine running indicates an open from fuel pump power circuit to PCM - fuel pump relay is not at fault.

3. Checking for proper control of the fuel pump relay by the PCM.

(Part 2 of 3)
4. Checking for open from fuel pump fuse to relay cavity "5."

5. Checking for open from relay pin "2" to ground.

6. This step checks the continuity of the complete fuel pump circuit from fuse "A1" through the fuel pump windings to ground. When the voltmeter is used to jumper the contact cavities of the relay connector, the voltmeter should read greater than 10 volts if the circuit is OK. If the circuit is OK, then the fuel pump relay is faulty.

7. If the relay or relay drive circuits are grounded, the PCM may be damaged by excessive current draw if battery voltage is over 16 volts. Repair the fault and check for proper operation.

8. Fault is most likely at PCM connector or PCM. Before PCM is replaced, check for damaged pins or a poor connection.

9. Refer to Wiring Diagrams for wiring details.

(Part 3 of 3)
10. At key "ON," the voltmeter should read greater than 10 volts for 2 seconds as the relay powers up the fuel pump.

11. If a short is present, it is in CKT 120, the fuel pump, or the PCM. Normal circuit resistance is 3 - 4 ohms.

12. If the voltmeter is a steady greater than 10 volts, then the non-switched portion of the fuel pump circuit is shorted.

13. Checking for PCM shorting 120 to ground.

14. Checking for a short inside the fuel tank.

15. Check fuel pump for shorts, check sender harness connector.

16. Checking for CKT 120 shorted to ground.

17. Check for grounded fuel pump prime connector, then connection at relay, oil pressure switch, then diagnose for harness shorted to ground.

NOTES ON INTERMITTENTS
If Code P020 is stored as history, unplug the oil pressure switch, start the engine, and allow to idle. Manipulate affected wiring, check the relay for proper installation into socket. If the fault is induced, the engine will stall, Code P020 will set. If Code P020 sets without an engine stall, the cause is a intermittent open CKT 120 between PCM pin "3E13" and fuel pump relay pin "3."

If the fuel pump circuit is grounded, the fuse will blow and P020 will set. Replace fuse, start engine and allow to idle. Manipulate affected wiring and connectors. If fault occurs, the fuse will blow and the engine will stall.