I'm installing a catback system on my 05 8. Im concerned about the engine light and passing inspections. Is there an ecu flash or tricking the system into thinking everything is normal at that o2 sensor? Any advice would be apreciated..

 

If you are installing a cat-back, then you are not moving, removing, etc... the O2 sensors at the cat.

If it is a catless midpipe that you are installing, then yes, the ECU might see the lack of a cat. Often it doesn't, but it's unpredictable. The only solid way of blocking the CEL is with a reflash that turns off the CEL. Typically done with an AccessPORT, although there are other methods now.

See the modding thread in my sig for info on that.