I have checked the OVP and it is the later part number, 000 540 67 45. It is the genuine Mercedes part and the date code is 1999 so it has been replaced in the past. I did a diode check with a multimeter when it was disconnected. That looked ok. I also checked voltage across all the pins with it connected and key on and all looked ok.

In using the meter to check voltage on the DTC, I see around 12v for pins 3, 8 and of course 16. But pin 14 shows around 7 volts. I wish I knew how to bench test the CC/ISC module so I could pull codes with it out of the car.