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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check stoplights. If stoplights do not function properly, repair as necessary and retest system. See EXTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT. If stoplights function properly, go to next step.
  2. Access ECM behind glove box. Turn ignition on. Backprobing ECM E5 connector, measure voltage between ground and terminal No. 15 (Green/Orange wire). See Figure. With brake pedal depressed, voltage should be 7.5-14.0 volts. With brake pedal released, voltage should be less than 1.5 volts. If voltage is not as specified, go to next step. If voltage is as specified, problem is intermittent.
  3. Check wiring harness between ECM E5 connector and stoplight switch. See WIRING DIAGRAMS article. Repair as necessary and retest system. If wiring harness is okay, replace ECM. Retest system.
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