The problem with dealers....is usually the extent of their work is servicing and washing cars. Now there are some exceptions, and there may me some very tach savvy people in them...but they are an exceptional rarity. Because with new cars...often they dont need a huge pile under warranty.
And when they do need something big, it's usually a case of remove old and fit a new part, rather than any actual intelligent or skilled work nevermind actual diagnostic work.
Which sadly for most is plugging in a computer and if it doesnt give a pinpoint answer ( which few ever do, or can do ), then they're stumped.