The pump is fed from a relay triggered when the ignition switch is on first position (and also by second position when engine is running).


Yes, you could agrue the pump is not part of the ABS but the ABS ECU will not say all is OK and turn out the dash lights unless the pressure is up (and some other checks pass too). The pump pressurises the fluid one side of the sphere against nitrogen on the other to maintain 2,000 psi. The pump should stop after 30 or so seconds on cold start up and less than a minute. If not, the pressure switch could have failed or the sphere may have. You cannot buy new spheres now - I found ne guy in USA who can repair them.



When one presses the brake pedal, the actuator (a big master cylinder) lets fluid to the calipers via the valve block. If the ECU detects locked wheels, it pulsates the valve blovk solenoids and you have ABS.


The wheel sensors are a common failure and will cause the ECU to fail its self-checks and you will not have ABS - yellow lights on. If pump OK, you will have brakes, though. If pump does not reach pressure, you will not have any brakes - red light on.


My binding issue is not sensors as they only effect the ABS pulsating. I have just sent all calipers away for refurb. If I still have binding issues, it can only mean a failed actuator - unheard of but could be. Having previously changed pump, actuator and ECU with no change, I hope my problem is calipers.