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Fuel Pump Control Circuit - IS300, LS430 & SC430 (Using Lexus Scan Tool)

NOTE: For information on engine immobilizer, see THEORY & OPERATION article.
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 - LEXUS article in GENERAL INFORMATION.
  1. Connect Lexus scan tool to DLC3. See Figure. Check fuel pump system operation. See FUEL PUMP OPERATION under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pump operates, go to step  8. If fuel pump does not operate, go to next step.
  2. Using Lexus scan tool, select ACTIVE TEST mode. Locate fuel pump relay in underhood relay block mounted in front of driver's side strut tower. Listen for noise while activating fuel pump relay. If relay noise can be heard when activated, go to step  4. If relay can not be heard when activated, go to next step.
  3. Check operation of fuel pump relay. See TESTING FUEL PUMP RELAY (IS300, LS430 & SC430)  in RELAYS under MOTORS, RELAYS & SOLENOIDS. Replace relay as necessary. If fuel pump relay is okay, go to next step.
  4. Check for faulty fuel pump. See FUEL PUMP RESISTANCE  and FUEL PUMP OPERATION (USING BATTERY VOLTAGE)  . Replace fuel pump as necessary. If fuel pump is okay, go to next step.
  5. Check operation of circuit opening relay. See TESTING EFI MAIN, STARTER & CIRCUIT OPENING RELAYS  in RELAYS under MOTORS, RELAYS & SOLENOIDS. Replace relay as necessary. If circuit opening relay is okay, go to next step.
  6. Check for open circuit in wiring or connectors between EFI main relay, circuit opening relay and ECM, between circuit opening relay and fuel pump relay, and between fuel pump relay and fuel pump. Also check for open circuit between fuel pump and ground. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Repair as necessary. If no problem is found, go to next step.
  7. Access ECM at left front of engine compartment. Turn ignition on. Measure voltage between ground and following ECM terminal:
    • On IS300, terminal No. 5 (Green/Yellow wire) at ECM connector E3. See Figure.
    • On LS430, terminal No. 14 (Green/Black wire) at ECM connector E3. See Figure.
    • On SC430, terminal No. 14 (Green/Black wire) at ECM connector E6. See Figure.

    If voltage is 9-14 volts, no problem is indicated at this time. If voltage is not 9-14 volts, locate and repair open circuit between battery and ECM terminal listed. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

  8. Locate fuel pump resistor under protective cover on driver's strut tower in engine compartment. Disconnect fuel pump resistor Black 2-pin connector. Measure resistance between resistor terminals. If resistance is not .30-.35 ohm at 68°F (20°C), replace resistor. If resistance is .30-.35 ohm, check for open circuit between fuel pump relay and fuel pump resistor, or fuel pump resistor and fuel pump. Repair as necessary. See appropriate WIRING DIAGRAMS article. If wiring is okay, replace ECM and retest.
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