P0141 code: 2002 A6 3.0L
 

I checked to codes after my check engine light came on and got a P0141. If that is one particular O2 sensor, is it easy to get to and change myself or should I take it to a mechanic and pay to get it done. Also, how do I know which sensor it is?

That would be "O2 sensor heater circuit bank 1 sensor 2": passenger side, after catalyst.
 

You can access it from the engine bay after taking out the airbox and the airway that goes to the engine, so it's not impossible to do yourself. Actually that's for an A4, but I'd imagine it being similar on the A6.