It is a cheap part ($20-$27 at Audi dealer), considered to be among the cheapest Audi parts... Access is not easy, but can be replaced in 30 minutes. As others have said, be sure to replace the rubber O-ring with it.
If you have trouble starting the car, ever, with no codes, this should be your #1 replacement part.
Also, I doubt engine washing affected this sensor, so don't be surprised if the issue pops up again shortly.
2005 AR 2.7 Black: GIAC stage 1, 710N, H-sport sway bars, Depo LED taillights
Past Audis: 2001 A6 4.2 | 2000 A4 1.8T Quattro 5-spd | 1993 100 CS Quattro | 1984 5000 CD turbo FWD