1998 Lexus SC 400FACTORY OEM SERVICE PROCEDURE

Position Sensor Power Source Circuit Test

NOTE: Use this procedure to check for problems in power supply circuit between driver's seat ECU and each position sensor.
  1. At driver's seat, remove bolts for front vertical adjuster. Lift front end of seat cushion slightly for access to driver's seat ECU (do not lift too far; harness clamp may come loose). Remove driver's seat ECU, leaving wiring harness connectors attached.
  2. Turn ignition on. While seat is moving (operate seat switch), measure voltage between chassis ground and driver's seat ECU connector "B", terminal No. 6 (Violet wire). See Figure.
  3. If voltage is 7-9 volts during switch operation, return to TROUBLE SHOOTING . If voltage is not 7-9 volts during switch operation, check for open or short in Violet wire between position sensors and ECU. See WIRING DIAGRAMS . If circuits are okay, replace driver's seat ECU.
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.