ELECTRONICALLY CONTROLLED BRAKE SYSTEM ABS Operates Before Necessary When Braking

DESCRIPTION

Troubleshooting for when ABS operates too soon due to a noisy signal from the speed sensor, a difference in output, etc.

PROCEDURE


  1. PERFORM TEST MODE (SIGNAL CHECK) INSPECTION (SPEED SENSOR CIRCUIT)


    1. Using the GTS, perform a Test Mode (Signal Check) inspection sensor check and check that speed sensor Test Mode (Signal Check) inspection items change from incomplete to complete.

      Click here


      Chassis > ABS/VSC/TRC > Utility
      Tester Display
      Signal Check
      OK
      Speed sensor Test Mode (Signal Check) inspection items change from incomplete to complete.
      Result
      Proceed to
      OK
      NG

    NG

    INSPECT AND REPAIR MALFUNCTIONING SPEED SENSOR CIRCUIT

    OK

  2. CHECK SPEED SENSOR AND SENSOR ROTOR SERRATIONS


    1. B004VZ9C31
      *a

      Component with harness connected

      (Skid Control ECU Assembly)
      *b Normal Signal Waveform

      Connect an oscilloscope to the front speed sensor terminal of the skid control ECU assembly and body ground.

    2. Check the waveform output when the wheels are rotated.

      OK
      The same waveform is output from all the sensors and there is no noise or interference in the waveform.

    3. Check that the waveform does not change while jiggling a connector or a wire harness.

      OK
      The waveform does not change.

      Tech Tips


      • As the vehicle speed (wheel revolution speed) increases, the waveform cycle narrows.

      • When noise is identified in the waveform on the oscilloscope, the erratic signals are likely due to speed sensor rotor scratches, looseness or attached foreign matter.

      Note


      • for AWD:

        When cleaning the front speed sensor, make sure to clean the installation hole before installation.

        Do not use parts cleaner when cleaning the front speed sensor rotor.


      • When cleaning the rear speed sensor, make sure to clean the installation hole before installation.

        Do not use parts cleaner when cleaning the rear speed sensor rotor.

      Tech Tips


      • for 2WD:

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

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

      • for AWD:

        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 the front axle hub sub-assembly.

      • The rear speed sensor rotor is incorporated into the rear axle hub and bearing assembly.

        If the rear speed sensor rotor needs to be replaced, replace the rear axle hub and bearing assembly.

      Result
      Result Proceed to
      OK (for Front (for 2WD)) A
      OK (for Front (for AWD)) B
      OK (for Rear) C
      NG D

    A

    REPLACE FRONT AXLE HUB SUB-ASSEMBLY for 2WD: Click here
    REPLACE FRONT AXLE HUB SUB-ASSEMBLY for AWD: Click here

    B

    CLEAN FRONT SPEED SENSOR AND FRONT SPEED SENSOR ROTOR

    C

    CLEAN REAR SPEED SENSOR AND REAR SPEED SENSOR ROTOR

    D

    CLEAN OR REPLACE MALFUNCTIONING SPEED SENSOR CIRCUIT