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Home >> Lexus >> 2003 >> IS 300 Base, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 103 (Cruise Control System) >> Diagnostic Tests >> DTC P1520/52: Stop Light Switch Circuit Malfunction >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Lexus IS 300. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: If not using the hand-held tester, start the inspection from step  2.
    NOTE: The stop light switch 1 has a function to disconnect the connection (OFF) when depressing the pedal, however, the ECM controls by the logic drivers, so with the hand-held tester, it displays ON. The stop light switch 1 indicates the input of connector E3 terminal No. 8 (ST1-) and the stop light switch 2 indicates the input of connector E4 terminal No. 4 (STP). See CONNECTOR IDENTIFICATION .
  1. Connect the hand-held tester to the DLC3. See Figure. Check the stop light switch using DATA LIST.
    • Brake Pedal Depressed -  The stop light switch 1 (Sub ECU), stop light switch 2 (Sub ECU) and stop light switch 2 (Main ECU) are ON.
    • Brake Pedal Released -  The stop light switch 1 (Sub ECU), stop light switch 2 (Sub ECU) and stop light switch 2 (Main ECU) are OFF.
    If the results are OK, proceed to the next circuit inspection of the symptom. See PROBLEM SYMPTOM INDEX  table. If the results are not good, go to the next step.
  2. Check that the stop light comes on when the brake pedal is depressed and turns off when the brake pedal is released. If the results are OK, go to the next step. If the results are not good, check the stop light system. See STOP LIGHT SWITCH CIRCUIT  under CIRCUIT TESTS and STOP LIGHT SWITCH  under COMPONENT TESTS.
  3. Remove the ECM with connectors still connected. Turn the ignition switch ON. Measure the voltage between connector E4 terminal No. 4 (STP) of the ECM connector and body ground, when the brake pedal is depressed (10-14 volts) and released (below 1 volt). If the results are OK, proceed to the next circuit inspection of the symptom. See PROBLEM SYMPTOM INDEX  table. If the results are not good, go to the next step.
  4. Remove the ECM with connectors still connected. Turn the ignition switch ON. Measure the voltage between connector E3 terminal No. 8 (ST1-) of the ECM connector and body ground, when the brake pedal is depressed and released. If the results are OK, proceed to the next circuit inspection of the symptom. See PROBLEM SYMPTOM INDEX  table. If the results are not good, go to the next step.
  5. Check the wiring harness and connector between connector E4 terminal No. 4 (STP) of the ECM and stop light switch, and connector E3 terminal No. 8 (ST1-) of the ECM and stop light switch. If the results are OK, check and replace the ECM. See ENGINE CONTROL MODULE (ECM)  under REMOVAL & INSTALLATION. If the results are not good, repair or replace the harness or connector.
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