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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Lexus LX 470. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check stoplight operation. If stoplights do not operate properly, repair as necessary and retest system. See appropriate wiring diagram in EXTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT. If stoplights operate properly, if using Lexus scan tool, go to next step. If not using Lexus scan tool, go to step  3.
  2. Connect Lexus scan tool to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on. Using scan tool, check STP signal. STP signal should be on when brake pedal is depressed, and go off when brake pedal is released. If STP signal is as specified, problem is intermittent. Check component and ECM connections. If STP signal is not as specified, go to step  4.
  3. Access ECM behind glove box. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between ground and terminal No. 15 (Green/White wire) at ECM harness connector E10. See Figure. Voltage should be 7.5-14.0 volts with brake pedal depressed and less than 1.5 volts with brake pedal released. If voltage is not as specified, go to next step. If voltage is as specified, problem is intermittent. Check component and ECM connections.
  4. Check for short in wiring between ECM and stoplight switch. If problem exists, repair wiring as necessary. If problem does not exist, replace ECM.
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