Circuit Description and Diagnostic Chart
SYSTEM: Fuel System CircuitWIRING DIAGRAM
CIRCUIT DESCRIPTION
Schematic View Of The Fuel Pump Control Circuit:
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 (ECM).
In the diagram below, 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 ECM, 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 ECM keeps Tr ON (circuit opening relay ON) and the fuel pump also keeps operating.
DIAGNOSTIC PROCEDURE
1. Check voltage at terminal FC.
^ If OK check and replace ECM.
^ If not OK proceed to step 2.
2. Check ECM power source circuit.
ECM Power Source Circuit
^ If OK proceed to step 3.
^ If not OK repair as necessary.
3. Check for circuit opening relay.
^ If OK proceed to step 4.
^ If not OK replace circuit opening relay.
4. Check for open in harness and connector between EFI main relay and circuit opening relay and ECM.
^ If OK proceed to step 5.
^ If not OK repair or replace harness or connector.
5. Check fuel pump.
^ If OK check for open in harness and connector between circuit opening relay and fuel pump and body ground.
^ If not OK Replace fuel pump.