My check engine light just turned on and the engine is lagging. I have a 2005 audi allroad wht could be the problem ?

Same happened to me and it was an ignition coil. There is a recall on these for several models. They will reimburse if you can't get it replaced by dealer, but takes time.
Check out audi owners site campaign section.
It was not a big deal to repair.

Check engine light means the computer system has picked up a problem which could affect performance. you need to access the data link to retrieve the code and then proceed thru a flow chart to repair

U need 2 take it 2 someone who has a analyser 2 find out the code