LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2000 >> GS 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Fuel System >> Fuel Delivery >> Fuel Pump Control Circuit (SC300 & SC400)
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Fuel Pump Control Circuit (SC300 & SC400)

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) - LS400, SC300 & SC400 . If fuel pump does not operate, go to next step. If fuel pump operates, go to step  6.
  2. Remove left rear quarter trim panel to access fuel pump Electronic Control Unit (ECU). It may be necessary to remove rear seat back and seat cushion to access ECU. Disconnect fuel pump ECU Black 5-pin connector. Turn ignition on. Measure voltage between ground and terminal No. 4 (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.
  3. With ignition switch turned to START position, measure voltage between terminals No. 1 (White/Black wire) and No. 3 (Red/White 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 Red/White wire between fuel pump ECU and ECM. Repair as necessary.
  5. Check fuel pump. See FUEL PUMP RESISTANCE (LS400, SC300 & SC400) . 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 Pink 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.
scientia non olet · About LEMON Manuals