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Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Lexus LX 470. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check if stop lights go on and off normally when the brake pedal is operated and released. Repair stop light circuit as necessary. If okay, go to next step.
  2. Remove the glove compartment door. Turn the ignition switch ON. Check the voltage between terminal STP and ST1- of the ECM connector and body ground. See Fig 1. See STOP LIGHT SWITCH VOLTAGE CHECK  table. If okay, check for intermittent problems. If not okay, go to next step.
    STOP LIGHT SWITCH VOLTAGE CHECK

    Brake Pedal Position Terminal STP Terminal ST1-
    Depressed 7.5-14 Volts Below 1.5 Volts
    Released Below 1.5 Volts 7.5-14 Volts
    Fig 1: Checking STP Signal
    G00239900Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  3. Check operation of stop light switch. Replace stop light switch as necessary. If okay, go to next step.
  4. Check harness and connector between ECM and stop light switch. Repair or replace harness or connector as necessary. If okay, check and replace ECM.
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