Ah yes the OVP. Stands for Over Voltage Protection relay. It's main function is to shunt the circuit whenever it senses a input voltage that is greater than nominal. Protects the sensitive computer circuitry.
Before you ask, it's located behind the battery. There is a black plastic shroud that you can just push forward and lift out of the way, which will reveal a few electrical components. The OVP is a silver rectangular unit with a clear plastic top, covering one or two red (or green) fuses inside, depending on your model year.
I replaced mine in my 300E a few months ago after getting some intermittent starting problems, and that cured it.
I have read threads where the OVP was the source of anything from starting problems to ABS light coming on.
Anyway, I am hardly an expert when it comes to this stuff, I can just share from experience. But if you do a search on "OVP", you should find a ton of information about it.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car