Modulador hidráulico del ABS defectuoso

The valve block that ABS uses to control brake pressure at each wheel independently — a set of inlet and outlet solenoid valves, a pump, and an accumulator, all in one casting.

Valves inside it are not separately serviceable on most vehicles, so a genuine valve failure means the assembly. That makes it expensive, and it makes the cheap checks worth doing properly first: the connector and harness live in the engine bay taking heat, vibration and salt, and they fail far more often than the valves.

Its commonest real failure is contamination rather than electrical. Brake fluid absorbs water over years; the corrosion and debris that follow are exactly the size to jam passages and valve seats that are measured in fractions of a millimetre. Fluid that has never been changed is a finding, not a footnote.

A valve stuck closed is more serious than one stuck open, because it can leave a wheel's brake applied — which drags, overheats and pulls the car to one side.