I have recently purchased a 1993 L reg Subaru Legacy Twin Cam Turbo. It has a problem with the ABS system which I think I may have diagnosed but perhaps someone else has had similar problems and could say if I am correct or not.

Upon starting the engine, the ABS warning light remains off. Braking is normal until under about 5mph when the pedal judders, accompanied by a twanging noise. (I have never had ABS before but suspect that this is the ABS operating). Although the brake pedal judders, the car comes to a halt normally. Once the car exceeds about 40mph, the ABS warning light activates and remains lit, at all speeds, until the engine is turned off. In this state, the brakes act normally although presumably the ABS has deactivated in a fail-safe mode.

I suspect that one of the ABS sensors on one of the wheels has malfunctioned and is sending spurious signals back to the control unit and that above 40mph, the unit recognises the signals to be spurious and disables the ABS system. If this is the case then I would just need to replace that sensor. Does this sound reasonable?

Thanks in advance for any help.

Robert.