IanIf the DTC clear and only come back after car is driven its unlikely to be the valve unit, if the fault will not clear at all i would suspect sticking valve or permanant electrical fault.
Had very simular fault but on 5 series, when ecu fails it always logs inlet valve fault and you loose the ability to activate componants etc
Do you have correct power supply to abs control unit ? and can you force run the pump ?
Does the car have two abs relays ? have seen problems with power up connections as one feeds the other. Shorted out abs sensors can cause faults within the system, Is the light on all the time ? or after being driven once cleared
Teves abs systems are SHI*E and give some very wierd problems
Chris