Failure after driving through puddle

[Nigel6065]

I've been searching the internet for a few weeks and had no success, possibly because I am asking the wrong questions.

A few weeks ago my son drove through a deep puddle at approximately 50km/hour and 200-300m later the car cutout. It's a 2004 X5 3.0D

I waited a couple of days thinking it would dry out, but with no success. There is a clicking sound behind the passenger footwell which sounds like a relay cycling. It is also showing fuel injector and transmission faults on the dash and dash lights and gauges are going crazy. For example temperature gauge bouncing from min to max. The engine cranks but doesn't start.

I've got access to a scanner but am not familiar with using it.

I would really appreciate some pointers as it probably isn't economically viable to take it to a mechanic or auto electrician