I’ve had a look around the forum as a lurker but not come across a similar thread so hoping to get a hiveminds take on my issues.
I’m the proud owner of a 2020 XC90 D420T2 MHEV (B5D I believe) R Design Pro which I’ve purchased a car from Copart UK with “flood” damage and sold as non runner. Good way to buy a new family car 
We’ve got the car home on a trailer (It was completely dead) and we’ve turned the engine by hand and dropped the oil to ensure it didn’t container water. We were also missing an airbox + MAF sensor which I’ve sourced and fitted.
After replacing the rear battery we saw life on the dash and everything working well inside, a turn of the starter and it tried to fire but no go however after a little easy start she fired and ran smooth on tick over and revved freely. We had various lights on the dash as you’d expect so we fired up a Launch code reader and cleared all codes to start with however on subsequent restarts after this – we might get a start but no throttle or very rough idle/no start. Then I’ll try again and it’ll start and rev with limp mode (Assuming it’s using default values)
We continually get these codes
P033600 – Crankshaft Position Sensor A Circuit Range/Performance General Failure Information
P133600 – Crankshaft/Camshaft Sensor Range/Performance
P061B64 – Internal Control Module Torque Calculation Performance Algorithm Based Failure, Signal Plausibility Failure
P119F68 – Reliability ECM Related Failure, Need to Be Repaired Basic Calculation Failure (Also P124968)
P060C48, P060A48, P061C48 – Internal Control Module – Main Processor Performance. System Internal Failures Supervision Software Failure
We’ve checked the Crankshaft Position Sensor and it’s connected ok (and no green wires) however I haven’t got a wiring diagram to check continuity, our next check was going to be ECU (ECM?) – Is it under the scuttle panel or on the left hand front wheel behind the bumper? Unfortunately we’ve got no way of finding out what kind of flood damage we are talking about – the way the engine sounds and revs when it’s letting me sounds good and it’s moved under it’s own steam enough that it felt “ok” which makes me hope it was more sat in water than running but I can’t rule it out.
I’m in IT Support Manager by trade, my father is a retired mechanic but has dealt with much older cars than this and I’m lucky enough to have 2 brother in laws who are full time mechanics so I’ve got some common sense between us (Besides me buying it) but if anyone has an idea of next steps to try I’m all ears.
Cheers for having a read and listening to the prattle!