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Home >> Lexus >> 2019 >> GX 460 Base >> Repair and Diagnosis >> Restraints >> Restraints Control Systems >> Pre-Collision System (Diagnostic Codes & Circuit Tests) >> Pre-Collision System >> DTC C1A4B: Stop Light Relay Circuit [08/2015 - 08/2019] >> Procedure
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DTC C1A4B: Stop Light Relay Circuit [08/2015 - 08/2019]: Procedure

  1. CHECK STOP LIGHT OPERATION 
    1. Check that the stop lights come on when the brake pedal is depressed and go off when the brake pedal is released.

      OK

      Condition Illumination Condition
      Brake pedal depressed On
      Brake pedal released Off

    Result: 

    NG 

    GO TO LIGHTING SYSTEM 

    (Refer to HOW TO PROCEED WITH TROUBLESHOOTING [08/2015 - 08/2019] )

    Result: 

    OK 

    See step  2

  2. CHECK TERMINAL VOLTAGE AND RESISTANCE (+B, GND) 
    1. Disconnect the A60 stop light control ECU connector.
    2. Measure the voltage according to the value(s) in the table below.
      GTY654199Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard Voltage

      Tester Connection Condition Specified Condition
      A60-6 (+B) - Body ground Always 11 to 14 V
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A60-8 (GND) - Body ground Always Below 1 Ω
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Stop Light Control ECU)

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  3

  3. CHECK TERMINAL VOLTAGE (STP) 
    1. Disconnect the A7 skid control ECU connector.
    2. Measure the voltage according to the value(s) in the table below.
      GTY680091Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard Voltage

      Tester Connection Switch Condition Specified Condition
      A7-7 (STP) - Body ground Brake pedal depressed 11 to 14 V
      Brake pedal released Below 1.5 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Skid Control ECU)

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  4

  4. CHECK TERMINAL VOLTAGE (STP) 
    1. Disconnect the A60 stop light control ECU connector.
    2. Measure the voltage according to the value(s) in the table below.
      GTY649708Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard Voltage

      Tester Connection Condition Specified Condition
      A60-5 (STP) - Body ground Brake pedal depressed 11 to 14 V
      Brake pedal released Below 1.5 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Stop Light Control Relay)

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  5

  5. PERFORM ACTIVE TEST USING TECHSTREAM (STOP LIGHT RELAY) 
    1. Connect the Techstream to the DLC3.
    2. Turn the engine switch on (IG).
    3. Turn the Techstream on.
    4. Enter the following menus: Chassis / ABS/VSC/TRC / Active Test.
      ABS/VSC/TRC

      Tester Display Test Part Control Range Diagnostic Note
      Stop Light Relay STOP LP relay Relay ON/OFF Observe the stop lights (do not come on for 2 to 5 seconds).
    5. While performing the Active Test, check the illumination condition of the stop lights and "Stop Light Relay Output" in the Data List.
      ABS/VSC/TRC

      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      Stop Light Relay Output STOP LP relay output/ ON or OFF ON: Relay output on (Stop lights on)
      OFF: Relay output off (Stop lights off)      		 -
      RESULT

      Result Proceed to
      When Active Test performed, Data List item changes between ON and OFF, but stop lights do not turn on A
      When Active Test performed, Data List item changes between ON and OFF and stop lights turn on and off B

    Result: 

    B 

    See step  7

    Result: 

    A 

    See step  6

  6. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL ECU - SKID CONTROL ECU) 
    1. Disconnect the A60 stop light control ECU connector.
    2. Disconnect the A7 skid control ECU connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A60-9 (ACC) - A7-16 (STPO) Always Below 1 Ω
      A60-9 (ACC) - Body ground Always 10 kΩ or higher

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (STOP LIGHT CONTROL ECU - SKID CONTROL ECU) 
    1. Disconnect the A60 stop light control ECU connector.
    2. Disconnect the A7 skid control ECU connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A60-1 (OUT) - A7-45 (STP2) Always Below 1 Ω

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. CHECK TERMINAL VOLTAGE (STP2) 
    1. Disconnect the A7 skid control ECU connector.
    2. Measure the voltage according to the value(s) in the table below.
      GTY671498Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      Standard Voltage

      Tester Connection Condition Specified Condition
      A7-45 (STP2) - Body ground Brake pedal depressed 11 to 14 V
      Brake pedal released Below 1.5 V
      TEXT IN ILLUSTRATION

      *a Front view of wire harness connector
      (to Skid Control ECU)

    Result: 

    NG 

    REPLACE STOP LIGHT CONTROL ECU ASSEMBLY 

    (Refer to REMOVAL [08/2015 - ] )

    Result: 

    OK 

    See step  9

  9. CHECK FOR DTC (PRE-COLLISION SYSTEM) 
    1. Turn the engine switch off and wait for at least 2 minutes.
    2. Clear the DTCs (Refer to DTC CHECK / CLEAR [08/2015 - 08/2019] ).
    3. Make sure that the DTC detection conditions are met.

      HINT: 

      If the detection conditions are not met, the system cannot detect malfunctions.

      • Using the Techstream, perform the Active Test "Stop Light Relay" with the engine switch on (IG).
    4. Check for DTCs (Refer to DTC CHECK / CLEAR [08/2015 - 08/2019] ).
      NOTE:

      When replacing the driving support ECU, always replace it with a new one and be sure to perform initialization (Refer to INITIALIZATION [08/2015 - 08/2019] ). If an ECU which was installed to another vehicle is used, the information stored in the ECU will not match the information from the vehicle, and as a result, a DTC may be stored.

      OK

      DTCs C1A4B are not output.

    Result: 

    OK 

    END 

    Result: 

    NG 

    REPLACE DRIVING SUPPORT ECU 

    (Refer to REMOVAL [08/2015 - 08/2019] )

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