Check engine light answer
The light would come on about every two weeks and go off again within a few days. It turns out the problem was the coolant temp. sensor. It was replaced under warranty.
I also complained about a pulsation in the brakes and they resurfaced the rear rotors. That cured the problem. All under warranty with excellent service in and out the same day. In addition, they gave me a brand new A6 loaner with the 3.0 engine. Nice car. It's no allroad, but it was a nice ride.
Hope this helps anyone with the mysterious check engine light problem.



