They are right, could be Bulb or Relay, the only 2 fail-safes in the system.
If its under Warranty, take a Beer+Deck chair, Relax, its their money their spending, not yours?
Replace bulb - 30min MAX = $20-50 (in Aus)
Just watchem if they say, wait your 'widget' needs fixing, and your Foofer valve needs adjustment...blah, blah, blah. Then the bill goes up+up?
Think like McDonalds, u go in for a burger and come out with Extra fries, UpSized etc etc. Basically more poor? Whenu didnt need it in the 1st place.
Oh and ALLWAYS ask for the replaced parts, most mechanics wont dodge you, but some will 'Replace' a part, and not actually have done it.
Beleive me when i say i KNOW TRUSTWORTHY mechanics who do this!!
Good luck.
> : )