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Home >> Toyota >> 2021 >> Highlander LE, 4WD >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Electronically Controlled Brake System (Except HV) - Diagnostic Codes (2 Of 3) >> ELECTRONICALLY CONTROLLED BRAKE SYSTEM (for Gasoline Model) >> DTC C137B-A2: Brake System Control Module "A" System Voltage System Voltage Low [11/2023 - ] >> Procedure

DTC C137B-A2: Brake System Control Module "A" System Voltage System Voltage Low [11/2023 - ]: Procedure

  1. CHECK HARNESS AND CONNECTOR (+BS TERMINAL) 
    1. Make sure that there is no looseness at the locking part and the connecting part of the connectors.
      GTY869229Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid Control ECU (Brake Actuator Assembly))

      OK

      The connector is securely connected.

    2. Disconnect the A39 skid control ECU (brake actuator assembly) connector.
    3. Check both the connector case and the terminals for deformation and corrosion.

      OK

      No deformation or corrosion.

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

      Standard Voltage

      Tester Connection Condition Specified Condition
      A39-14 (+BS) - Body ground Always 11 to 14 V

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  2

  2. CHECK HARNESS AND CONNECTOR (IG1 TERMINAL) 
    1. Turn the ignition switch to ON.
      GTY869230Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Front view of wire harness connector
      (to Skid Control ECU (Brake Actuator Assembly))
    2. Measure the voltage according to the value(s) in the table below.

      Standard Voltage

      Tester Connection Condition Specified Condition
      A39-45 (IG1) - Body ground Ignition switch ON 10.5 to 16 V*1
      11 to 14 V*2
      1. *1: w/ Stop and Start System
      2. *2: w/o Stop and Start System

      Result

      Result Proceed to
      OK A
      NG (w/ Stop and Start System) B
      NG (w/o Stop and Start System) C

    Result: 

    B 

    INSPECT STOP AND START SYSTEM (BACKUP BOOST CONVERTER CIRCUIT). Refer to  Backup Boost Converter Circuit [11/2023 - ] 

    Result: 

    C 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    A 

    See step  3

  3. CHECK HARNESS AND CONNECTOR (GND1 TERMINAL) 
    1. Turn the ignition switch off.
    2. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A39-1 (GND1) - Body ground 1 minute or more after disconnecting the cable from the negative (-) auxiliary battery terminal Below 1 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  4

  4. CLEAR DTC 
    1. Reconnect the A39 skid control ECU (brake actuator assembly) connector.
    2. Clear the DTCs.

      Chassis > Brake/EPB > Clear DTCs 

    3. Turn the ignition switch off.

      Result

      Proceed to
      NEXT

    Result: 

    NEXT 

    See step  5

  5. RECONFIRM DTC 
    1. Based on the Freeze Frame Data and interview with the customer, attempt to reproduce the conditions when the malfunction occurred.
    2. Check if the same DTC is output.

      Chassis > Brake/EPB > Trouble Codes 

      Result

      Result Proceed to
      DTC C137B-A2 is not output. A
      DTC C137B-A2 is output. B

    Result: 

    A 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [12/2019 - ] 

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [11/2023 - ] 

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