2015 DS5 (Pre-facelift) displaying UREA warning

[joshgame]

I have bought a 2015 DS5 on the weekend from an independent dealership and in true new car fashion, it has issues after driving it the 2 hours back home.

When on the test drive, it gave no indication of errors or faults whatsoever but is now warning me that I have 600 miles to top up the AdBlue before the engine will no longer start.

After reading the handbook, it seems this warning should come about if you ignore previous warnings for long enough...

I'm wondering, after filling up the AdBlue reservoir with the right 22241 stuff, what the most likely cause for the error is and if there's anything I should do myself or have a garage do?
With my Bluetooth OBD reader, it reports a NOx sensor fault but I'm thinking that may be a false-read if there is something in the relating systems that's wrong instead.

Any advice would be appreciated.

P.s. I know that this is one of the few common issues with these cars and was hoping it wouldn't rear it's head within 24 hours....

[RichardW]

If it came on with 700 miles to go, then it's a fault, not just low level which comes on at 1500 miles. If you bought it from a dealer then it's on them to fix it...

[joshgame]

I thought as much.

Unfortunately I'm not going to be able to go back to the dealer any time in the next couple of weeks so they've agreed to pay any costs for work I have done closer to home.

Is there anything in particular that I should request a garage take a look at rather than just asking them to generally 'diagnose this'? Or, is there anything I can do/check immediately myself in order to rule something out?