I just got my TT a few weeks ago and my check engine light came on so I took it to auto zone. The rep said it was the secondary sensor. From research online I'm seeing that it could just be the filter that needs to be cleaned or replaced causing the light to come on or possibly an air leak somewhere. My car is not rough idling or anything. (the light went away for a few days then came back) Does anyone know where I can find a video showing the steps to get to this filter. The only directions I have been able to find were on ehow and I don't trust that site! http://www.ehow.com/how_5463275_clea...af-sensor.html

Thanks for the help!

 

If you are talking about the seconday O2 sensor (after the cat), its purpose is to check on the condition of the cat and is not involved in controlling the A/F mixture. However, your cat is not doing its job and may eventually clog, in which case it would cause the engine to run poorly.