Engine Systems fault displays after 15 seconds of turning key 1.6 tdci

Good morning everyone, hope you're all enjoying your vehicles.

We buy cars for different purposes throughout our lives. My 2007 Focus 1.6 tdci 90 was bought to swallow work miles and I fell in love with it. Don't know why, it is guttless! But I'm still will it 4 years and 100k miles later with literally no hiccups, just regular servicing. It has a total of 170k on the clock.

I got in it last morning and it sounded like it was struggling starting. It turned over a couple more times than i've become used to (fairly instant). I got a few miles up the road and was met with 'engine systems failure' on the LCD and a red light at the bottom near the speedo. The car entered limp mode. I pulled over, switched off and back on again, it was clear. A few miles down the road the same thing.

It bounces off the limiter at 3krpm and produces some white smoke leaving a black stain on the floor.

Without turning the car over but switching the key to the on position the engine systems failure appears after exactly 15 seconds without failure every time. If I turn the engine on within this time it won't appear til a few miles down the road. It is like it looking for feedback from something within 15 seconds, not seeing it and notifying me.

OBD shows either one or two errors. Both N/A and sometimes a U0073 P but I think that might be a red herring. Another potential red herring is that I don't hear the fuel pump prime, but not sure if I ever have. I do hear that noise when the engine is switched off though.

I'm really struggling here guys, when the car runs without this fault everything seems OK. Bit of a clicking/tapping noise coming from top of engine that has been there for maybe 10k miles now.