Quote:
Originally Posted by Mike Noc
Had the same problem and found it was caused by a pattern sensor not quite being near enough to the magnetic reluctor ring on the bearing. Worked fine at speed but when the wheel was rotating slowly it started missing the odd segment.
Cleaned the backplate and made sure the sensor was seated correctly but still had to file around a mm off the back of the sensor bracket to sort it.
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That would be something a scope would easily identify.
Going back to basics...
The ABS is triggered, because it sees enough of a difference in rotation speed between one or more of the wheels. The usual cause of a difference being that wheels being braked are slipping on the road surface, so to maintain grip and balance, it reduces the braking effect on the wheels sufficient to get the rotational speeds to match.
Under inflated tyres, excess movement in the suspension and similar can all cause the ABS to trigger when it should not. As also can the sensor simply not responding at low speed as pointed out by Mike above, or metallic dirt on the ring producing distorted or extra pulses.