the secondary air injection system is a smog controll for cold starts.

when the car is cold so is the catalytic converter and the the cat needs to be hot in order to filter out harmful exhaust gas effectively. the air pump mixes in atmospheric air into the exhaust gas stream before the cat to help the cat heat up to max effeciency faster.

What the secondary air injection system consists of is a coolant temp sensor, a valve, and an air pump. when the car is cold the coolant temp sensor basically trips the air pump to turn on and open's the combination or "combi" valve. very often on cars over or near 100k miles is one gets carbon buildup in the combi valve and it causes to stop working.

if that is not the trouble like stated above, then either the coolant temp sensor is bad or the actual pump is broken, which is pricey.

diy solution: find the combi valve (search audiforums), and clean it with some carburator cleaner. then find the air pump, and send some electricity through the pump and see if it pumps. then check the fuse. if everything is ok then clear the code and see if it comes back. if it does then its probably time for a new coolant temp sensor.

 

My "check engine" light has been on for months. I had a shop replaced the air hosts and tube, replaced the O2 sensor ans spend almost $1,000, but the check engine light came back on again. The error code is P0171 and the car would not pass emission test. One other option is to fix is the MAF sensor. I am trying to do it myself (clean it), but I could not locate it. I had removed the covers and look at the air intake that goes to the engine, but I could not recognize the MAF sensor to remove it. Can any one help? Thanks!

 

I drive an 06 A4 2.0T sedan approx 105,000kms on it. First time owning an Audi and need some help!!!

Engine light came on out of nowhere, so had it checked with an odbII reader.
DTC 02,I/M NO. Fuel trim,bank1 system too lean. No idea what that could be. Friend reseted it for me, engine light came off. Few hours later came back on.

Started it and noticed engine running sluggish sounds extremely louder than normal. About 5mins after running it started smelling like gasoline. Been trying to follow numerous forums not exactly sure what to do from here.

No pan heater, transmission flush not completed yet, still under warranty power train. Recently got a warranty extension sent from Audi re: recall for the Intake manifold runner control motor, "fuel pressure sensor (G410), and positive crankcase ventilation (PCV) Valve. Just curious whether this would be in relation to the engine light coming on and Dtc p0171 code being the fault code.

IN NEED OF SOME SERIOUS HELP GUYS, as can't bring my vehicle in Audi dealership until 2wks.

 

My check engine came on and is still on I it use high end gas and is maintained every 4000 mile and could it be my spark plugs