Occasionally when applying a very low brake pedal pressure at medium speeds my ABS brakes will start chattering. Increasing the pressure causes the chattering to cease. Letting up on the pressure and then reapplying pressure usually also makes the chattering go away. Otherwise the braking is totally normal - no shuddering, no squealing, no pulling to one side, no wheels locking. This happens on any surface and in any conditions ( dry paved roads ). No brake warning light comes on. It is like there is a "sweet" spot just at the beginning of the pedal range. Anybody has any ideas where to start looking ?


  • Welcome to Motor Vehicle Maintenance & Repair! Commented Sep 2, 2018 at 21:35

1 Answer 1


Peter, best place to begin your diagnosis is to physically inspect each independent wheel speed sensor. There is a sensor attached to each of the 4 wheels to monitor their independent speed which uses this information to activate the Anti-lock Brake System (ABS).

For example: If all your wheels except say your Left Front are reading 35 mph but your Left Front is reading 20 mph, the vehicle detects this as a problem and activated the ABS system at an attempt to bring all 4 wheel speeds to near exact speed of each other, were talking fraction of MPH.

Inspected the sensors for any rust or if they are not sitting flush to their mounting surface, if there is rust on its mounting point then you need to remove the rust, reinstall the sensors and road test it to verify your repairs.

If you have rust on the vehicle then this may become a challenging task, especially if you are not mechanically inclined and lack patience when something goes awry as the worst possible time.

  • I will indeed do a thorough inspection of everything as soon as I can find the time. What I find puzzling though is why the pulse train from one or more sensors sometimes doesn't come on at low pedal pressure only to come back at higher pressure. And why all 4 are always present at high pressure. I can't believe there are 4 separate switches / relays involved which leaves something mechanical like the distance between a sensor and its ring varying with pressure . Is that even possible ? Any ideas ?
    – peter
    Commented Sep 3, 2018 at 0:48

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