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Brake Warning Light Remains ON [04/2018 - 08/2020]: Procedure

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  1. CHECK CAN COMMUNICATION SYSTEM 
    1. Check if CAN communication system DTCs are output.

      Refer to HOW TO PROCEED WITH TROUBLESHOOTING [04/2018 -]

      Result

      Result Proceed to
      DTCs are not output A
      DTCs are output B

    Result: 

    B 

    INSPECT CAN COMMUNICATION SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [04/2018 -] 

    Result: 

    A 

    See step  2

  2. CHECK IF BRAKE ACTUATOR ASSEMBLY CONNECTOR IS SECURELY CONNECTED 
    1. Check if the skid control ECU (brake actuator assembly) connector is securely connected.

      OK

      The connector is securely connected.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    CONNECT CONNECTOR TO BRAKE ACTUATOR ASSEMBLY CORRECTLY 

    Result: 

    OK 

    See step  3

  3. CHECK BATTERY 
    1. Check the battery voltage.

      Standard Voltage

      Tester Connection Condition Specified Condition
      Positive (+) terminal - Negative (-) terminal Engine switch off 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    CHECK OR REPLACE CHARGING SYSTEM COMPONENT OR BATTERY. Refer to  ON-VEHICLE INSPECTION [04/2018 -] 

    Result: 

    OK 

    See step  4

  4. CHECK HARNESS AND CONNECTOR (POWER SOURCE TERMINAL) 
    1. Turn the engine switch off.
      GTY908216Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid Control ECU (Brake Actuator Assembly))
    2. Make sure that there is no looseness at the locking part and the connecting part of the connector.

      OK

      The connector is securely connected.

    3. Disconnect the A28 skid control ECU (brake actuator assembly) connector.
    4. Check both the connector case and the terminals for deformation and corrosion.

      OK

      No deformation or corrosion.

    5. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A28-30 (+BS) - Body ground Always 11 to 14 V
      A28-36 (IG1) - Body ground Engine switch on (IG) 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (POWER SOURCE CIRCUIT) 

    Result: 

    OK 

    See step  5

  5. CHECK HARNESS AND CONNECTOR (GND1 TERMINAL) 
    1. Turn the engine switch off.
      GTY908217Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid Control ECU (Brake Actuator Assembly))
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A28-46 (GND1) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR (GND1 CIRCUIT) 

    Result: 

    OK 

    See step  6

  6. INSPECT BRAKE MASTER CYLINDER RESERVOIR ASSEMBLY 
    1. Turn the engine switch off.
      GTY759731Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component without harness connected
      (Brake Fluid Level Warning Switch (Brake Master Cylinder Reservoir Assembly))
    2. Reconnect the A28 skid control ECU (brake actuator assembly) connector.
    3. Remove the reservoir filler cap and strainer.
    4. Make sure that there is no looseness at the locking part and the connecting part of the connector.

      OK

      The connector is securely connected.

    5. Disconnect the A1 brake fluid level warning switch (brake master cylinder reservoir assembly) connector.
    6. Check both the connector case and the terminals for deformation and corrosion.

      OK

      No deformation or corrosion.

    7. Measure the resistance according to the value(s) in the table below.

      HINT: 

      A float is located inside the reservoir. Its position changes according to the brake fluid level.

      Standard Resistance

      Tester Connection Condition Specified Condition
      1 (+) - 2 (E) Switch off (float up) 1.9 to 2.1 kΩ
      1 (+) - 2 (E) Switch on (float down) Below 1 Ω
    8. If there is no problem after finishing the above check, adjust the brake fluid level to the MAX level.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE BRAKE MASTER CYLINDER RESERVOIR ASSEMBLY. Refer to  DISASSEMBLY [04/2018 -] 

    Result: 

    OK 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (COMBINATION METER ASSEMBLY - BRAKE MASTER CYLINDER RESERVOIR ASSEMBLY) 
    1. Make sure that there is no looseness at the locking part and the connecting part of the connector.

      OK

      The connector is securely connected.

    2. Disconnect the G16 combination meter assembly connector.
    3. Check both the connector case and the terminals for deformation and corrosion.

      OK

      No deformation or corrosion.

    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      G16-12 (SW) - A1-1 (+) Always Below 1 Ω
      G16-12 (SW) or A1-1 (+) - Body ground Always 10 kΩ or higher
      A1-2 (E) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. INSPECT VACUUM WARNING SWITCH ASSEMBLY 
    1. Reconnect the A1 brake fluid level warning switch (brake master cylinder reservoir assembly) connector.
    2. Reconnect the G16 combination meter assembly connector.
    3. Inspect the vacuum warning switch assembly.

      Refer to ON-VEHICLE INSPECTION [04/2018 - 08/2020]

      OK

      The vacuum warning switch assembly is normal.

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE VACUUM WARNING SWITCH ASSEMBLY 

    Result: 

    OK 

    See step  9

  9. CHECK HARNESS AND CONNECTOR (COMBINATION METER ASSEMBLY - VACUUM WARNING SWITCH ASSEMBLY) 
    1. Make sure that there is no looseness at the locking part and the connecting part of the connector.

      OK

      The connector is securely connected.

    2. Disconnect the A2 vacuum warning switch assembly connector.
    3. Disconnect the G16 combination meter assembly connector.
    4. Check both the connector case and the terminals for deformation and corrosion.

      OK

      No deformation or corrosion.

    5. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      G16-7 (VCM) - A2-2 (+) Always Below 1 Ω
      G16-7 (VCM) or A2-2 (+) - Body ground Always 10 kΩ or higher
      A2-1 (E) - Body ground Always Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  10

  10. READ VALUE USING TECHSTREAM (BRAKE WARNING LIGHT) 
    1. Reconnect the A2 vacuum warning switch assembly connector.
    2. Reconnect the G16 combination meter assembly connector.
    3. Enter the following menus: Chassis / ABS/VSC/TRAC/EPB / Data List.

      Chassis > ABS/VSC/TRAC/EPB > Data List 

      Tester Display Measurement Item Range Normal Condition Diagnostic Note
      Brake Warning Light Brake system warning light (red indicator) ON or OFF ON: Warning light on
      OFF: Warning light off      		 -

      Chassis > ABS/VSC/TRAC/EPB > Data List 

      Tester Display
      Brake Warning Light
    4. Check the Techstream display condition of the brake system warning light (red indicator).

      Result

      Result Proceed to
      The value of Brake Warning Light is ON A
      The value of Brake Warning Light is OFF B

    Result: 

    A 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [04/2018 - 08/2020] 

    Result: 

    B 

    INSPECT METER / GAUGE SYSTEM. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [04/2018 -] 

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