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Home >> Lexus >> 1998 >> GS 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Fuel System >> Fuel Pump Control Circuit >> LS400
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Fuel Pump Control Circuit: LS400

  1. Check fuel pump operation. See FUEL PUMP OPERATION . If fuel pump operates, go to step 6). If fuel pump does not operate, go to next step.
  2. Check fuel pump relay. See RELAYS  under MODULES, MOTORS RELAYS & SOLENOIDS. Replace relay as necessary. If relay is okay, go to next step.
  3. Remove trim cover from behind rear seat in luggage compartment. Disconnect 2-pin fuel pump connector (NOT sending unit connector). Measure resistance between female terminals of fuel pump connector. Resistance should be 0.2-3.0 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace fuel pump.
  4. Check circuit opening relay. See RELAYS  under MODULES, MOTORS RELAYS & SOLENOIDS. Replace relay as necessary. If relay is okay, check for open in wiring harness between main relay and fuel pump or between fuel pump and ground. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, go to next step.
  5. Measure voltage between chassis ground and terminal No. 4 (Green/Black wire) of ECM E12 connector. See Figure-10. If voltage is 9-14 volts, no problem is indicated at this time. If voltage is not 9-14 volts, locate and repair open between battery and ECM.
  6. Disconnect fuel pump resistor located in left front of engine compartment. Measure resistance between resistor terminals. If resistance is not .70-.76 ohm, replace resistor. If resistance is .70-.76 ohm, check for open circuit between fuel pump relay and fuel pump resistor, or fuel pump resistor and fuel pump. Repair as necessary.
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