Today I broke down and took my 97 850 T5 in to have the ABS system diagnosed. My symptoms have included ABS going off when not appropriate and occasional illumination of ABS light. I can tell the ABS is going off because occasionally the car shakes violently when braking, but not always. It seems especially prevelant after a rainstorm. Sometimes the brakes seem to shake sllightly at higher speeds.

Based on threads here I expected the dealer to tell me I needed ABS ECU. However, instead he blamed a faulty ABS pump. I don't see how this could be the case with the car shuddering when stopping. I have also read in some threads that this code can be an indication of faulty ECU when pump actually works. Also he stated that the ECU would need to be replaced if the pump did not correct the problem to the tune of $2000 total.

Does anyone know of a optest I can perform on the pump to verify operation? I would like to just purchase a $400 ecu and be done with it but don't want to take the chance unless I am certain the pump works.