At noon today, my wife dropped off the van and they told her there would be a charge of $250+HST for the service.
You have an issue under warranty.
Let them try to be the experts they so often come across as...diagnose the problem and stop guessing...anybody can do that.
Tell them to take a hike!
Well, I did pay in the end under the condition that if the problem persists, they replace the transmission and I get my money back.
Interestingly enough, in his email the service mgr said Hyundai requires transmission to be flushed every 160,000km but since Canada is considered to be the zone with "severe driving conditions"

(ever been to Siberia?) they
recommend that the interval be cut in half. I call that BS but don't want to argue over $275 and then be stuck with a $5,000 (or whatever) transmission bill.
I am driving to Montreal next week with a full load (4 adults, 2 kids and a pile of suitcases,
Cozumel here I come!! 
) so I'll see if the check engine lights up again after the flush.
The dealership also assured me that, even after the warranty runs out, since I have a history with them, should the transmission fail the goodwill warranty repair would be honoured. I tend to believe people until they screw me (fool me once, shame on you...)
Regarding the warranty, to their defense they never alluded or hinted that I might have a problem with warranty repair. It's something that I myself brought up as, strictly speaking, they could do it (deny it if you can't prove regular maintenance) if they wanted to. It may be the same across the industry, I don't know.
I would still recommend this service shop over Bank St. Hyundai
