Description and Diagnosis Procedure

SYSTEM: Fuel Pump Control Circuit

CIRCUIT DESCRIPTION





The Fuel Pump is switched on (low voltage at terminal FC) when STA is on or while the NE signal is input to the Engine Control Module. In the diagram, when the engine is cranked, current flows from terminal ST of the Ignition Switch to the starter relay coil, the starter relay switches on and current flows to coil L1 of the Circuit Opening Relay. Thus the Circuit Opening Relay switches on, power is supplied to the Fuel Pump and the Fuel Pump operates. When the STA signal and NE signal are input to the Engine Control Module, Tr is turned ON, current flows to coil L2 of the Circuit Opening Relay, the relay switches on and the Fuel Pump operates. While the NE signal is generated (engine running), the Engine Control Module keeps Tr ON (Circuit Opening Relay ON) and the Fuel Pump also keeps operating.





DIAGNOSTIC PROCEDURE USING LEXUS HAND HELD TESTER
1. Check Fuel Pump operation.
- If not OK proceed to step 2.
- If OK proceed to step 4.
2. Check for Engine Control Module power source circuit.
- If OK proceed to step 3.
- If not OK repair or replace.
3. Check Fuel Pump.
- If OK check for open in harness and connector between terminal FP of Data Link ConnectorI and Fuel Pump. Fuel Pump and body ground.
- If not OK repair or replace fuel pump.
4. Connect the LEXUS hand - held tester and check operation of Fuel Pump.
- If not OK proceed to step 5.
- If OK proceed to step 7.
5. Check Circuit Opening Relay.
- If OK proceed to step 6.
- If not OK replace Circuit Opening Relay.
6. Check voltage terminal FC.
- If OK check and replace Engine Control Module.
- If not OK check for open in harness and connector between EFI Main Relay and Circuit Opening Relay, Circuit Opening Relay and Engine Control Module.
7. Check Circuit Opening Relay.
- If OK proceed to step 8.
- If not OK replace Circuit Opening Relay.
8. Check voltage terminal 3 of Circuit Opening Relay.
- If OK check for open in harness and connector between terminal 6 of Circuit Opening Relay and body ground.
- If not OK check starter signal circuit.

DIAGNOSTIC PROCEDURE USING OBDII SCAN TOOL
1. Check Fuel Pump operation.
- If not OK proceed to step 2.
- If OK proceed to step 4.
2. Check Engine Control Module power source circuit.
- If OK proceed to step 3.
- If not OK repair or replace.
3. Check Fuel Pump.
- If OK Check for open in harness and connector between terminal FP of Data Link ConnectorI and Fuel Pump, Fuel Pump and body ground.
- If not OK repair or replace Fuel Pump.
4. Check Circuit Opening Relay.
- If OK proceed to step 5.
- If not OK replace Circuit Opening Relay.
5. Check voltage terminal FC.
- If not OK proceed to step 6.
- If OK check and replace Engine Control Module.
6. Check for open in harness and connector between EFI Main Relay and Engine Control Module.
- If OK proceed to step 7.
- If not OK repair or replace harness or connector.
7. Check voltage terminal 3 of Circuit Opening Relay.
- If OK check for open in harness and connector between terminal 6 of Circuit Opening Relay and body ground.
- If not OK check starter signal circuit.