We all know our car will not replicate when it hits the service lot. Two things may help...
1. In your case, take a snapshot of the warning. Regardless if they find a code, they can't deny the warning if you have a pic or vid. Email it to them.
2. Feel free to contact VCNA directly via the website. Give the service mgr a fair shot first. I've had pretty good luck with going direct to NA.
I had a litany of issues with my '12 that even had the engine pulled with a new flywheel and starter installed.
Through it all, used videos (burned to CD & given to svs mgr), emailed pics, notes/TSBs found here on Swedespeed (this was the most helpful) and mails directly to VCNA.
And a measure of patience.
Found if you help them to the logical path that they were way more receptive to help find "where's Waldo" - whatever the mysterious issue. But I had to do a lot of research and talk with people here who are a lot smarter on these things than I. This worked with 2 shops on the Volvo and 1 shop with our Toyota. All were very appreciative. Got new bakes and rotors all the way around on the 4Runner while 20,000 mi out of warranty, it works. And we didn't have to be an arse to do it, quite the opposite. We were part of the team.
YMMV