Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1999 Lexus SC 400FACTORY OEM SERVICE PROCEDURE
Checking Fuel Pump Operation Using Scan Tool (LS400)
- Connect scan tool to data link connector No. 3. See Figure. Turn ignition on. DO NOT start engine.
- Turn scan tool on. Select ACTIVE TEST mode on scan tool. Using scan tool manufacturer's instructions, activate fuel pump. Listen for fuel pump operating sound and feel for fuel pressure in fuel inlet line to rear of the fuel rails.
- Turn ignition off. Remove scan tool. If fuel pump operates, check fuel pressure. See FUEL PRESSURE . If fuel pump does not operate, EFI main relay, circuit opening relay, fuel pump relay or fuel pump resistor may be defective. For explanation of relays and fuel pump resistor operation, see FUEL PUMP CONTROL CIRCUIT . For testing of relays and fuel pump resistor, see appropriate SYSTEM & COMPONENT TESTING article.
- If EFI main relay, circuit opening relay, fuel pump relay or fuel pump resistor are okay, check for defective fuses, fusible links or wiring. See appropriate wiring diagram in WIRING DIAGRAMS article. If fuses, fusible links and wiring are okay, check for defective fuel pump. See CHECKING FUEL PUMP OPERATION BY APPLYING BATTERY VOLTAGE TO FUEL PUMP . If problem exists in fuel pump relay or control circuit, Diagnostic Trouble Code (DTC) P1200 may be stored in Engine Control Module (ECM). See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article for retrieving of DTCs.
Factory Service Tools
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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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