ABS Operates Before Necessary When Braking [03/2017 - ]: Procedure

1. Using the Techstream, 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.

   Refer to TEST MODE PROCEDURE [03/2017 - 05/2023] , or refer to TEST MODE PROCEDURE [05/2023 - ]

   Chassis > ABS/VSC/TRAC > Utility 

   Tester Display
   Signal Check

   OK

   Speed sensor Test Mode (Signal Check) inspection items change from incomplete to complete.

   Result

   Proceed to
   OK
   NG

Result: 

NG 

INSPECT AND REPAIR MALFUNCTIONING SPEED SENSOR CIRCUIT 

Result: 

OK 

See step  2

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

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a	Component with harness connected (Skid Control ECU Assembly)
   *b	Normal Signal Waveform

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.

   HINT: 

   • 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:

   • 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.

   HINT: 

   • 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.

   • 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)	A
   OK (for Rear)	B
   NG	C

Result: 

A 

REPLACE FRONT AXLE HUB SUB-ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - 09/2023]  , or refer to  REMOVAL [09/2023 - ] 

Result: 

B 

CLEAN REAR SPEED SENSOR AND REAR SPEED SENSOR ROTOR 

Result: 

C 

CLEAN OR REPLACE MALFUNCTIONING SPEED SENSOR CIRCUIT