When it all boils down, the OVP affects the system by not powering the control units involved. The easiest way to figure this and to truely evaluate the system is to watch the EHA current. If the problem exists, electrically, then it manifests itself through the current control of EHA. If there is no current the first suspect is the OVP. If there is any current, it is not the OVP. Pretty simple.
Bosch Master, ASE Master, L1
33 years MB technician