Hopefully somebody can help me.

At the moment by car turns over but won't start, I have a 2014 audi Q3 2.0 diesel.
The car is reading -46 on temp gauge, on dash it says fuel system failure and is only getting 3.9 volts to my tank.
Somebody has told me this could be the BCM as they are sure this runs all these things, has anybody seen this before or have any ideas if the guy i spoke too is correct?

Any advice would be gratefully received.

Thanks

Joe