I don't know about the check valve; haven't had to learn everything about these cars yet. I'd guess it's incorporated in the fuel pump(s).

I like Arthur's suggestion. Use the search feature of the board to read up on 'm104 ovp'. Find the old and new OVP part numbers, then see which you have. If old, a replacement is called for. The OVP supplies power to the engine and ABS computers. If it is on the fritz, the car definately won't run.

- JimY