2014 Q5 TDI - MIL comes on intermittently, usually in damp weather. No driving issues, nor unusual feel, noises, etc to the vehicle. The first time that this happened, the dealer identified a problem with the AdBlue pump seal and replaced it. No consistent relationship to fuelling/gas cap. I've moved and am now a client at a different service place (Audi). The intermittent MIL still occurs and I am told that I must bring it in when the MIL is on in order to diagnose. Problem: by the time that I can take the vehicle in/get an appt, the MIL has turned off. Am told by service desk person that the stored fault codes can't identify the problem or why the MIL is intermittently coming on. Surely this cannot be so!

Thoughts, opinions, concerns, answers?

Thanks.