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Fuel Pump Control Circuit (GS300 & GS400)

CAUTION: If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION.
  1. Check fuel pump operation. See FUEL PUMP OPERATION (USING BATTERY VOLTAGE) - GS300 & GS400 . If fuel pump does not operate, go to next step. If fuel pump operates, go to step  6.
  2. Remove trunk trim cover from behind rear seat in luggage compartment. Disconnect fuel pump Electronic Control Unit (ECU) 10-pin connector in left side of luggage compartment. Turn ignition on. Measure voltage between ground and terminal No. 10 (Black/Red wire) at fuel pump ECU connector. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, check for open or short in wiring harness between EFI main relay and fuel pump ECU. See appropriate wiring diagram in WIRING DIAGRAMS article.
  3. With ignition switch turned to START position, measure voltage between terminals No. 5 (White/Black wire) and No. 8 (Black/Blue wire) at fuel pump ECU. If voltage is 3.3-4.3 volts, go to step  5. If voltage is not 3.3-4.3 volts, go to next step.
  4. Check for open or short in White/Black wire between fuel pump ECU and ground. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If White/Black wire is okay, check for open or short in Black/Blue wire between fuel pump ECU and ECM. Repair as necessary.
  5. Check fuel pump. See FUEL PUMP RESISTANCE (GS300 & GS400) . Replace fuel pump as necessary. If fuel pump is okay, check for an open circuit in wiring harness between fuel pump ECU and fuel pump. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace fuel pump ECU and retest.
  6. Check for an open or short in Black/Red wire between fuel pump ECU and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, replace ECM and retest.
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