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DTC P0504-2B: Brake Switch "A"/"B" Signal Cross Coupled [09/2022 - 09/2024]: Procedure

WARNING: This page is about a different car, the 2025 Toyota GR Corolla, 2024 Toyota GR Corolla, and 2023 Toyota GR Corolla. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK TERMINAL VOLTAGE (POWER SOURCE OF STOP LIGHT SWITCH ASSEMBLY) 
    1. Disconnect the stop light switch assembly connector.
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A53-7(B) - Body ground Always 11 to 14 V
      GTY1108909Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Stop Light Switch Assembly)

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - BATTERY) 

    Result: 

    OK 

    See step  2

  2. CHECK TERMINAL VOLTAGE (POWER SOURCE OF STOP LIGHT SWITCH ASSEMBLY) 
    1. Disconnect the stop light switch assembly connector.
    2. Turn the ignition switch to ON.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A53-6(B) - Body ground Ignition switch ON 11 to 14 V
      GTY1105866Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Stop Light Switch Assembly)

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - NO. 1 INTEGRATION RELAY) 

    Result: 

    OK 

    See step  3

  3. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - BODY GROUND) 
    1. Disconnect the stop light switch assembly connector.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A53-2 (GND) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  4

  4. CHECK TERMINAL VOLTAGE (STP AND ST1- VOLTAGE) 
    GTY809790Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    *a Brake Pedal Depressed
    *b Brake Pedal Released
    1. Disconnect the ECM connector.
    2. Turn the ignition switch to ON.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Brake Pedal Operation Specified Condition
      A139-22 (ST1-) - Body ground Released 7.5 to 14 V
      Depressed Below 1.5 V
      A139-21 (STP) - Body ground Released Below 1.5 V
      Depressed 7.5 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE ECM 

    Refer to REMOVAL [09/2022 - 11/2022] , or refer to REMOVAL [11/2022 - 09/2024]

    Result: 

    NG 

    See step  5

  5. CHECK HARNESS AND CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - ECM) 
    1. Disconnect the stop light switch assembly connector.
    2. Disconnect the ECM connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A53-5(L) - A139-22 (ST1-) Always Below 1 Ω
      A53-3(L) - A139-21 (STP) Always Below 1 Ω
      A53-5(L) or A139-22 (ST1-) - Body ground and other terminals Always 10 kΩ or higher
      A53-3(L) or A139-21 (STP) - Body ground and other terminals Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE STOP LIGHT SWITCH ASSEMBLY 

    Refer to REMOVAL [06/2018 - ]

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STOP LIGHT SWITCH ASSEMBLY - ECM) 

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