Yes, we are sure is the valve block... It's just that the mechanic is surprised that my ABS light didn't come on. He says that others with the same problem did light on, and it's strange that mine does not.

 

It depends what is failing in the valve block. There are two common causes.

One is the deterioration and breakage of parts of the ribbon circuit that controls the valves. When this happens, random valve actuation (or lack of it) can happen.

The other fault is where tiny bits of sediment can lodge under the "release" valve for a wheel circuit, so that once it opens in abs conditions, to preclude further brake pressure to that wheel, it then fails to seat back and close, although the system thinks everything is fine. This then means that no further brake application happens on that wheel. So the harder you continue to brake, the more the car dives to the opposite side of the road. Very unpleasant!

Hope that helps

Paul