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.
1990 Lexus LS 400FACTORY OEM SERVICE PROCEDURE
Theft Deterrent Ecu
- Turn ignition off. Disconnect theft deterrent ECU connectors. Theft deterrent ECU is located under dashboard, left of steering column. Turn ignition switch to START position. Place transmission in Neutral. Using a DVOM, check for battery voltage between terminal No. 1 of 18-pin connector and ground. See Fig 1.
- If battery voltage is not present, repair harness and connector between starter relay and theft deterrent ECU. If battery voltage is present, go to next step.
- Turn ignition off. Connect theft deterrent ECU connectors. Using a DVOM, measure resistance between theft deterrent ECU connector terminal No. 14 of 18-pin connector and ground. See Fig 1. Resistance should be one ohm or less.
- If resistance is within specification, replace ECU with a known good unit and retest system. If resistance is not within specification, disconnect theft deterrent ECU connector.
- Check theft deterrent ECU ground terminal and wire harness connector for damage. Repair as necessary. If theft deterrent ECU ground terminal and wire harness connector are okay, replace theft deterrent ECU and retest system.
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.
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 QuoteNo obligation. See pricing before you book.