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Home › Lexus › 1997 › SC 400 › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes › Circuit Tests › DTC P1520 - Stoplight Switch Signal Malfunction › Diagnosis & Repair

Diagnosis & Repair

  1. Check stoplights. If stoplights do not function properly, repair as necessary and retest system. If stoplights function properly, go to next step.
  2. Access ECM harness connectors behind glove box. Connect Check Harness "A" (SST 09990-01000) to ECM. See TEST PREPARATION under SELF-DIAGNOSTIC SYSTEM. Turn ignition on. Measure voltage between ground and terminal No. 4 (Green/White wire) at ECM "A" connector. With brake pedal depressed, voltage should be 7.5-14.0 volts. With brake pedal released, voltage should be less than 1.5 volt. If voltage is not as specified, go to next step. If voltage is as specified, check wire harness and connectors. Problem is intermittent.
  3. Check for short in wiring harness between ECM and stoplight switch. Repair as necessary and retest system. If wiring harness is okay, replace ECM. Retest system.
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