2012 Nissan Altima automatic with only 45,000 miles. About 2 months ago the car started exhibiting a noticeable power loss in local driving. Took it to the local mechanic who said it might be the transmission, but the local transmission place said the transmission was fine but saw wheel sensor codes they reset and told me to see what it does. No change in power but when I took it on the highway and after about 10 minutes the car would not go above 60mph and then wouldn't go above 40mph. Service engine light flickered. I took it to the dealer and after two weeks they tell me they can't figure it out unless the service engine light to comes on as there were no codes generated. No idea where to go from here on a car that's been maintained and has low mileage.
It sounds like the dealer just let the car sit for two weeks and no doubt charged you a king's ransom for their trouble. They didn't even bother looking at data? Could be a lot of things. Take it to a good independent mechanic who will actually take the trouble to analyze the problem. (NOT a chain shop like Pep Boys, Firestone, Midas, etc.)
