1999 Lexus SC 400FACTORY OEM SERVICE PROCEDURE

ECM Power Source Circuit (Ignition Keyed): LS400

  1. Access ECM behind glove box. Turn ignition on. Backprobing connector, connect DVOM negative lead to terminal No. 17 (White/Black wire) at ECM E13 connector and positive lead to terminal No. 16 (White wire) at ECM E15 connector. See Fig 1. If 9-14 volts is present, ECM power circuit is okay. Diagnose by symptom. See TROUBLE SHOOTING - NO CODES article. If 9-14 volts is not present, go to next step.
  2. Check for an open circuit in White/Black wire between ground and terminal No. 17 at ECM E13 connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If wiring is okay, go to next step.
  3. Measure voltage between chassis ground and terminal No. 9 (Black/Orange wire) at ECM E15 connector. If 9-14 volts is present, go to step  5. If 9-14 volts is not present, check IGN fuse in instrument panel junction box under left side of instrument panel.
  4. If fuse is blown, repair cause of blown fuse. If fuse is okay, check ignition switch. See STEERING COLUMN SWITCHES article in ACCESSORIES & EQUIPMENT. Replace ignition switch as necessary and retest. If ignition switch is okay, repair open circuit between battery and ignition switch, or between ignition switch and ECM.
  5. Turn ignition on. Measure voltage between chassis ground and terminal No. 10 (Light Green wire) at ECM E15 connector. If 9-14 volts is not present, replace ECM. If 9-14 volts is present, check EFI No. 1 fuse located in engine compartment fuse/relay box at left front of engine compartment. If fuse is okay, go to next step. If fuse is blown, repair cause of blown fuse.
  6. Check EFI main relay located in engine compartment fuse/relay box at left front of engine compartment. See RELAYS  under MOTORS, RELAYS & SOLENOIDS. If EFI main relay is okay, check circuit between chassis ground and terminal No. 10 at ECM E15 connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If circuit is okay, repair circuit between battery and EFI No. 1 fuse.
Fig 1: Identifying Electronic Control Module (ECM) Connector Terminals (LS400)
G98E11530Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.