There must be a thousand posts on this.
The OVP is just a power supply relay. It makes NO decisions except that it filters voltage spikes and prevents an overvoltage to the control units. Most of the time it is not intermittant. It can be tested by seeing if the control units have power. The easiest way to do that is to test the output at pin#3. If any output good or bad occurs the system is working and the OVP has done its job.
The one intermittant I have seen is a voltage drop through the unit caused usually by a high resistance connection where the output terminal attached to the printed circuit. Measuring the voltage at the output is the most definative test but is a lot harder to get at.
Bosch Master, ASE Master, L1
33 years MB technician