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Diagnosis & Repair (Using OBD-II Scan Tool)

WARNING: This page is about a different car, the 2003 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check if the stop lights go on and off normally when the brake pedal is operated and released. If okay, go to next step. If not okay, repair stop light circuit.
  2. Turn the ignition switch ON. Measure voltage between terminal E1 of ECM E3 connector and terminal STP of ECM E5 connector. See Figure. With brake pedal depressed, 7.5-14 volts should be present. With brake pedal released, less than 1.5 volts should be present. If okay, check for intermittent problems. If not okay, go to next step.
  3. Disconnect the D2 driver side junction block ECU 18-pin connector. See Figure. Disconnect the ECM E5 connector. See Figure. Check continuity between the wire harness side connectors. See DRIVER SIDE JUNCTION BLOCK/ECM CONTINUITY  table. If continuity is to specification, check and replace ECM. If continuity is not to specification, repair or replace harness or connector as necessary.
    DRIVER SIDE JUNCTION BLOCK/ECM CONTINUITY

    Terminals Specification
    STPO (D2-12) - STP (E5-4) Continuity
    STPO (D2-12) Or STP (E5-4) - E1 (E3-7) No Continuity
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