It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. You will need a scan tool to retrieve codes stored in the computer of your car. I'm guessing there is a code or cods stored, even if there wasn't with a professional grade scan tool you can read live sensor data without having to do intrusive testing at each sensor. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online Perhaps look at Audi specific forums see if anyone would know of a common problem but a scan tool is the first place to start.