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 GS 400FACTORY OEM SERVICE PROCEDURE
Headlight Control Switch Circuit
NOTE:
If LEXUS scan tool is available, start test from step 1. If this scan tool is not available, start test from step 2.
- Using scan tool, check headlight control switch using DATA LIST. If headlight switch is faulty, go to next step. If headlight switch is okay, go to next test listed in appropriate SYMPTOM DIAGNOSIS table under TROUBLE SHOOTING .
- Check headlight control switch. See STEERING COLUMN SWITCHES article. Replace headlight control switch as necessary. Retest system operation. If headlight control switch is okay, go to next step.
- Check circuits for faults between headlight control switch and body control ECU No. 2. See WIRING DIAGRAMS . Repair or replace as necessary. If circuits are okay, go to next test listed in appropriate SYMPTOM DIAGNOSIS table under TROUBLE SHOOTING .
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.