Taillights stay always on Lexus IS200/IS300

INFO: Applies to Lexus IS200/IS300 from 1999 to 2005 with AUTO headlights system and ambient light sensor.

Problem Symptoms

• Taillights stay always on, even if:
  • ignition is set to off,
  • drivers side door is opened,
  • car is locker via remote or key,
  • car is over the bright light.
• Tailights stay always on, stay on for some minutes/hours, are flashing.

Problem Cause

This problem can be caused by:

• moisture and corrosion in connectors or wires,
• bad Body ECU,
• bad Theft Deterrent ECU,
• bad Solar Sensor.

Problem Mitigation

1. The source of moisture in cabin have to be localized and removed. It can be bad windshield seal, bad seals between engine compartment and cabin, bad door seals, plugged AC vents drain.
2. All wires and connectors to all ECU’s have to be checked/cleaned/repaired.
3. Alle ECU’s have to be checked for corrosion/burnt elements. They can be easily opened and are not hard to do that.
4. Drivers side (LHD) junction box have to be examined for corrosion. To open, it has to be drilled in place of plastic studs holding two halfs.
5. The operation of solar sensor should be checked. It also dimms cabin light and can be monitored through OBDII.
6. After all of that, the taillights should turn off automatically.