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Home >> Lexus >> 2019 >> LS 500 Base, AWD >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Electronically Controlled Brake System (W/ Vacuum Brake Booster) - Diagnostic Codes (3 Of 4) >> ELECTRONICALLY CONTROLLED BRAKE SYSTEM (w/ Vacuum Brake Booster) >> DTC C1426: Stop Light Switch OFF Stuck Malfunction [12/2017 - 09/2018] >> Procedure

DTC C1426: Stop Light Switch OFF Stuck Malfunction [12/2017 - 09/2018]: Procedure

  1. CHECK BRAKE PEDAL HEIGHT AND STOP LIGHT SWITCH ASSEMBLY INSTALLATION 
    1. Check the brake pedal height and stop light switch assembly installation.

      Refer to INSTALLATION [12/2017 - 10/2023]

      OK

      The brake pedal height and stop light switch assembly installation are normal.

      HINT: 

      If the on/off status of the stop light switch assembly and the pressure increase information from the master cylinder pressure sensor do not match due to an improperly installed brake pedal or stop light switch assembly, this DTC may be stored. Therefore, be sure to check the installation condition of the pedal and stop light switch assembly before inspecting the input signals and other related parts.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    ADJUST BRAKE PEDAL HEIGHT OR STOP LIGHT SWITCH ASSEMBLY INSTALLATION. Refer to  ADJUSTMENT [12/2017 - 10/2020] 

    Result: 

    OK 

    See step  2

  2. 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

      Proceed to
      OK
      NG

    Result: 

    NG 

    See step  9

    Result: 

    OK 

    See step  3

  3. READ VALUE USING TECHSTREAM (STOP LIGHT SW AND BRAKE PEDAL LOAD SENSING SW) 
    1. Connect the Techstream to the DLC3.
    2. Turn the engine switch on (IG).
    3. Select the Data List using the Techstream.

      Refer to DATA LIST / ACTIVE TEST [12/2017 - 09/2018]

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display Measurement Item Range Normal Condition Diagnostic Note
      Stop Light SW Stop light switch assembly ON or OFF ON: Brake pedal depressed
      OFF: Brake pedal released      		 -
      Brake Pedal Load Sensing SW Brake pedal load sensing switch ON or OFF ON: Brake pedal depressed beyond a specified point
      OFF: Brake pedal not depressed beyond a specified point      		 -

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display
      Stop Light SW
      Brake Pedal Load Sensing SW
    4. Check that the stop light switch display and brake pedal load sensing switch display observed on the Techstream change according to brake pedal operation.

      OK

      The Techstream displays ON or OFF according to brake pedal operation.

    5. Slowly depress the brake pedal, and check when the stop light switch assembly and brake pedal load sensing switch turn on.

      OK

      First the stop light switch assembly should turn on, and then the brake pedal load sensing switch should turn on.

      Result

      Result Proceed to
      OK A
      NG (The stop light switch assembly does not turn on.) B
      NG (Turning on of the brake pedal load sensing switch is not confirmed.) C
      NG (The brake pedal load sensing switch turns on first.) D

    Result: 

    B 

    See step  5

    Result: 

    C 

    See step  7

    Result: 

    D 

    REPLACE BRAKE PEDAL SUPPORT ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

    Result: 

    A 

    See step  4

  4. RECONFIRM DTC 
    1. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [12/2017 - 09/2018]

      Chassis > ABS/VSC/TRAC > Clear DTCs 

    2. Turn the engine switch off.
    3. Start the engine.
    4. Depress the brake pedal several times to test the stop light circuit.
    5. Check if the same DTC is output.

      Refer to DTC CHECK / CLEAR [12/2017 - 09/2018]

      Chassis > ABS/VSC/TRAC > Trouble Codes 

      Result

      Result Proceed to
      DTC C1426 is not output. A
      DTC C1426 is output. B

    Result: 

    A 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [12/2017 - 09/2018] 

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

  5. CHECK HARNESS AND CONNECTOR (STP TERMINAL) 
    1. Turn the engine switch off.
    2. Make sure that there is no looseness at the locking part and the connecting part of the connector.
    3. Disconnect the A9 skid control ECU (brake actuator assembly) connector.
    4. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A9-35 (STP) - Body ground Stop light switch assembly on (Brake pedal depressed) 8 to 14 V
      A9-35 (STP) - Body ground Stop light switch assembly off (Brake pedal released) Below 1.5 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STP CIRCUIT) 

    Result: 

    OK 

    See step  6

  6. CHECK HARNESS AND CONNECTOR (GND1 TERMINAL) 
    1. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A9-25 (GND1) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (GND1 CIRCUIT) 

  7. INSPECT BRAKE PEDAL SUPPORT ASSEMBLY 
    1. Inspect the brake pedal load sensing switch (brake pedal support assembly).

      Refer to ON-VEHICLE INSPECTION [12/2017 - 10/2023]

      OK

      The brake pedal load sensing switch (brake pedal support assembly) is normal.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE BRAKE PEDAL SUPPORT ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

    Result: 

    OK 

    See step  8

  8. CHECK HARNESS AND CONNECTOR (BRAKE ACTUATOR ASSEMBLY - BRAKE PEDAL SUPPORT ASSEMBLY) 
    1. Make sure that there is no looseness at the locking part and the connecting part of the connector.
    2. Disconnect the A9 skid control ECU (brake actuator assembly) connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A9-23 (FSW+) - A5-2 (FSW+) Always Below 1 Ω
      A9-23 (FSW+) or A5-2 (FSW+) - Body ground Always 10 kΩ or higher
      A5-1 (FSW-) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  9. INSPECT STOP LIGHT SWITCH ASSEMBLY 
    1. Inspect the stop light switch assembly.

      Refer to ON-VEHICLE INSPECTION [12/2017 - ]

      OK

      The stop light switch assembly is normal.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE STOP LIGHT SWITCH ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

    Result: 

    OK 

    See step  10

  10. CHECK HARNESS AND CONNECTOR (STP TERMINAL) 
    1. Make sure that there is no looseness at the locking part and the connecting part of the connector.
    2. Disconnect the A9 skid control ECU (brake actuator assembly) connector.
    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A9-35 (STP) - Body ground Stop light switch assembly on (Brake pedal depressed) 8 to 14 V
      A9-35 (STP) - Body ground Stop light switch assembly off (Brake pedal released) Below 1.5 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (STP CIRCUIT) 

    Result: 

    OK 

    See step  11

  11. RECONFIRM DTC 
    1. Reconnect the A9 skid control ECU (brake actuator assembly) connector.
    2. Clear the DTCs.

      Refer to DTC CHECK / CLEAR [12/2017 - 09/2018]

      Chassis > ABS/VSC/TRAC > Clear DTCs 

    3. Turn the engine switch off.
    4. Start the engine.
    5. Depress the brake pedal several times to test the stop light circuit.
    6. Check if the same DTC is output.

      Refer to DTC CHECK / CLEAR [12/2017 - 09/2018]

      Chassis > ABS/VSC/TRAC > Trouble Codes 

      Result

      Result Proceed to
      DTC C1426 is not output. A
      DTC C1426 is output. B

    Result: 

    A 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [12/2017 - 09/2018] 

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [12/2017 - 09/2018] 

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