I was told by the Audi technician during an oil change that they noticed a knock sensor problem that generated a check engine light that came on for a few days and then went out. I haven't had anything done for it yet. 2011 Q7 TDI
Low oil indicator light comes on when engine cold - parked on level surface. Oil is not low but light remains on until engine is warm.
NOX sensor comes on and the goes off and then back on again. It is not flashing but showing solid illumination for hours and then goes out and then comes back on. Shop says replace it for about 4-5 hundred but warned, "It might come right back on."
Nox Sensor (the 1st of 2) failed at 62,000 miles. Engine light illumination was the only indication. No performance issues noted. Again had a Nox failure at 85,000 miles. Both times the repair cost over $900. This MUST be related to the VW/Audi/Porsche emissions fiasco that is underway. I think both repairs should have been covered as a warranty repair.