1999 Lexus SC 300FACTORY OEM SERVICE PROCEDURE

Fuel Pump Control Circuit (LS400)

  1. Check fuel pump operation. See FUEL PUMP OPERATION (USING BATTERY VOLTAGE) - LS400, SC300 & SC400 . 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 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 fuel pump Dark Gray 2-pin connector located near rear speaker. See Figure. Measure resistance between fuel pump connector terminals (component side). 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 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. 5 (Green/Black wire) at ECM E15 connector. 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 between battery and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article.
  6. Locate fuel pump resistor in left front corner of engine compartment. Disconnect fuel pump resistor Black 2-pin connector. Measure resistance between resistor terminals. If resistance is not .70-.76 ohm at 68°F (20°C), 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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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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