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Home >> Lexus >> 2021 >> 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 C1401: Front Speed Sensor RH Malfunction; DTC C1402: Front Speed Sensor LH Malfunction [12/2017 - 09/2018] >> Procedure

DTC C1401: Front Speed Sensor RH Malfunction; DTC C1402: Front Speed Sensor LH Malfunction [12/2017 - 09/2018]: Procedure

  1. CHECK FRONT SPEED SENSOR INSTALLATION 
    1. Turn the engine switch off.
    2. for 2WD:

      Check the speed sensor installation.

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

      OK

      There is no clearance between the sensor and the front steering knuckle.

      GTY806226Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *A for 2WD
      *B for AWD
      *a No clearance
      *b Correct
      *c Incorrect

      for AWD:

      Check the speed sensor installation.

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

      OK

      There is no clearance between the sensor and the front steering knuckle.

      The installation bolt is tightened properly.

      Result

      Proceed to
      OK (for 2WD)
      OK (for AWD)
      NG (for 2WD)
      NG (for AWD)

    Result: 

    OK (for AWD) 

    See step  5

    Result: 

    NG (for 2WD) 

    REPLACE FRONT AXLE HUB SUB-ASSEMBLY. Refer to  REMOVAL [12/2017 - ] 

    Result: 

    NG (for AWD) 

    INSTALL FRONT SPEED SENSOR CORRECTLY. Refer to  INSTALLATION [12/2017 - 10/2023] 

    Result: 

    OK (for 2WD) 

    See step  2

  2. READ VALUE USING TECHSTREAM (FRONT SPEED SENSOR) 
    1. Connect the Techstream to the DLC3.
    2. Start the engine.
    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
      FR Wheel Speed Front wheel speed sensor RH reading Min.: 0 km/h (0 mph), Max.: 326 km/h (202 mph) Vehicle stopped: 0 km/h (0 mph) When driving at constant speed: No large fluctuations
      FL Wheel Speed Front wheel speed sensor LH reading Min.: 0 km/h (0 mph), Max.: 326 km/h (202 mph) Vehicle stopped: 0 km/h (0 mph) When driving at constant speed: No large fluctuations

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display
      FR Wheel Speed
      FL Wheel Speed
    4. Check the speed value output from the speed sensor displayed on the Techstream.

      HINT: 

      Factors that affect the indicated vehicle speed include tire size, tire pressure, and tire wear. The speed indicated on the speedometer has an allowable margin of error. This can be tested using a speedometer tester (calibrated chassis dynamometer). For details about testing and the margin of error, see the reference chart.

      Refer to OPERATION CHECK [12/2017 - 10/2020]

      OK

      The speed value output from the speed sensor displayed on the Techstream is similar to the speed indicated on the speedometer.

      Result

      Result
      OK
      NG

      HINT: 

      The front speed sensor rotor and front speed sensor are incorporated into the front axle hub sub-assembly.

      If the front speed sensor rotor needs to be replaced, replace the front axle hub sub-assembly with front speed sensor.

    Result: 

    OK 

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

    Result: 

    NG 

    See step  3

  3. INSPECT FRONT SKID CONTROL SENSOR WIRE 
    GTY817524Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    *A for RH
    *B for LH
    *1 Front Skid Control Sensor Wire
    *a Front view of wire harness connector
    (to Vehicle Side Connector)
    *b Front view of wire harness connector
    (to Sensor Side Connector)
    1. Make sure that there is no looseness at the locking part and the connecting part of the connectors.
    2. Disconnect the z21, A16, A25 and/or AA3 front skid control sensor wire connector.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      FOR RH

      Tester Connection Condition Specified Condition
      z21 -1 (FR+) - A25 -5 (FR+) Always Below 1 Ω
      z21 -1 (FR+) or A25 -5 (FR+) - Body ground and other terminals Always 10 MΩ or higher
      z21 -2 (FR-) - A25 -1 (FR-) Always Below 1 Ω
      z21 -2 (FR-) or A25 -1 (FR-) - Body ground and other terminals Always 10 MΩ or higher
      FOR LH

      Tester Connection Condition Specified Condition
      A16 -2 (FL+) - AA3 -3 Always Below 1 Ω
      A16 -2 (FL+) or AA3 -3 - Body ground and other terminals Always 10 MΩ or higher
      A16 -1 (FL-) - AA3 -1 Always Below 1 Ω
      A16 -1 (FL-) or AA3 -1 - Body ground and other terminals Always 10 MΩ or higher
      NOTE:

      Check the speed sensor signal after replacement.

      Refer to TEST MODE PROCEDURE [12/2017 - 09/2018]

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE FRONT SKID CONTROL SENSOR WIRE. Refer to  REMOVAL [12/2017 - ] 

    Result: 

    OK 

    See step  4

  4. CHECK HARNESS AND CONNECTOR (BRAKE ACTUATOR ASSEMBLY - FRONT SKID CONTROL SENSOR WIRE) 
    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

      FOR RH

      Tester Connection Condition Specified Condition
      A9-31 (FR+) - A25-5 (FR+) Always Below 1 Ω
      A9-31 (FR+) or A25-5 (FR+) - Body ground Always 10 kΩ or higher
      A9-30 (FR-) - A25-1 (FR-) Always Below 1 Ω
      A9-30 (FR-) or A25-1 (FR-) - Body ground Always 10 kΩ or higher
      FOR LH

      Tester Connection Condition Specified Condition
      A9-18 (FL+) - AA3 -3 Always Below 1 Ω
      A9-18 (FL+) or AA3 -3 - Body ground Always 10 kΩ or higher
      A9-17 (FL-) - AA3 -1 Always Below 1 Ω
      A9-17 (FL-) or AA3 -1 - Body ground Always 10 kΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    REPLACE FRONT AXLE HUB SUB-ASSEMBLY. Refer to  REMOVAL [12/2017 - ] 

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

  5. CHECK FRONT SPEED SENSOR (CHECK FOR FOREIGN MATTER) 
    1. Remove the front speed sensor.

      Refer to REMOVAL [12/2017 - ]

    2. Check the front speed sensor tip.

      OK

      The sensor tip is free of scratches, oil, and foreign matter.

      NOTE:
      • If there is oil or foreign matter on the speed sensor, clean the speed sensor.
      • If the speed sensor is damaged, replace the speed sensor with a new one.
      • Check the speed sensor signal after cleaning or replacement.

        Refer to TEST MODE PROCEDURE [12/2017 - 09/2018]

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    CLEAN OR REPLACE FRONT SPEED SENSOR 

    Result: 

    OK 

    See step  6

  6. READ VALUE USING TECHSTREAM (FRONT SPEED SENSOR) 
    1. Connect the Techstream to the DLC3.
    2. Start the engine.
    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
      FR Wheel Speed Front wheel speed sensor RH reading Min.: 0 km/h (0 mph), Max.: 326 km/h (202 mph) Vehicle stopped: 0 km/h (0 mph) When driving at constant speed: No large fluctuations
      FL Wheel Speed Front wheel speed sensor LH reading Min.: 0 km/h (0 mph), Max.: 326 km/h (202 mph) Vehicle stopped: 0 km/h (0 mph) When driving at constant speed: No large fluctuations

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display
      FR Wheel Speed
      FL Wheel Speed
    4. Check the speed value output from the speed sensor displayed on the Techstream.

      HINT: 

      Factors that affect the indicated vehicle speed include tire size, tire pressure, and tire wear. The speed indicated on the speedometer has an allowable margin of error. This can be tested using a speedometer tester (calibrated chassis dynamometer). For details about testing and the margin of error, see the reference chart.

      Refer to OPERATION CHECK [12/2017 - 10/2020]

      OK

      The speed value output from the speed sensor displayed on the Techstream is similar to the speed indicated on the speedometer.

      Result

      Result
      OK
      NG

      HINT: 

      The front speed sensor rotor and front speed sensor are incorporated into the front axle hub sub-assembly.

      If the front speed sensor rotor needs to be replaced, replace the front axle hub sub-assembly with front speed sensor.

    Result: 

    OK 

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

    Result: 

    NG 

    See step  7

  7. CHECK HARNESS AND CONNECTOR (BRAKE ACTUATOR ASSEMBLY - FRONT SPEED SENSOR) 
    1. Install the front speed sensor and the component with the sensor rotor.
    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. Disconnect the A72 or A73 front speed sensor connector.
    5. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      FOR RH

      Tester Connection Condition Specified Condition
      A9-31 (FR+) - A73-5 (FR+) Always Below 1 Ω
      A9-31 (FR+) or A73-5 (FR+) - Body ground Always 10 MΩ or higher
      A9-30 (FR-) - A73-1 (FR-) Always Below 1 Ω
      A9-30 (FR-) or A73-1 (FR-) - Body ground Always 10 MΩ or higher
      FOR LH

      Tester Connection Condition Specified Condition
      A9-18 (FL+) - A72-3 (FL+) Always Below 1 Ω
      A9-18 (FL+) or A72-3 (FL+) - Body ground Always 10 MΩ or higher
      A9-17 (FL-) - A72-1 (FL-) Always Below 1 Ω
      A9-17 (FL-) or A72-1 (FL-) - Body ground Always 10 MΩ or higher

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPAIR OR REPLACE HARNESS OR CONNECTOR 

    Result: 

    OK 

    See step  8

  8. CHECK FRONT SPEED SENSOR ROTOR (CHECK FOR FOREIGN MATTER) 
    1. Remove the component with the speed sensor rotor.

      Refer to REMOVAL [12/2017 - 10/2022]

    2. Check the speed sensor rotor.

      OK

      The rotor is free of scratches, oil, and foreign matter.

      NOTE:
      • If there is oil or foreign matter on the speed sensor rotor, clean the speed sensor rotor.
      • If the speed sensor rotor is damaged, replace the speed sensor rotor with a new one.
      • Check the speed sensor signal after cleaning or replacement.

        Refer to TEST MODE PROCEDURE [12/2017 - 09/2018]

      HINT: 

      • The front speed sensor rotor is incorporated into the front axle hub sub-assembly.
      • If the front speed sensor rotor needs to be replaced, replace it together with the front axle hub sub-assembly.

      Result

      Result Proceed to
      OK A
      NG (The speed sensor rotor is damaged.) B
      NG (There is foreign matter on the speed sensor rotor.) C

    Result: 

    A 

    REPLACE FRONT SPEED SENSOR. Refer to  REMOVAL [12/2017 - ] 

    Result: 

    B 

    REPLACE FRONT AXLE HUB SUB-ASSEMBLY. Refer to  REMOVAL [12/2017 - 10/2022] 

    Result: 

    C 

    CLEAN FRONT SPEED SENSOR ROTOR 

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