Error code P0411
What is the best way to find outwhether the secondary air pump and the combi valves are okay?

 

I have the same issue- a P0411 error code - I'd start checking the vacuum hose. Mine had a hole in it. One thing I am not sure is if the A4/A6 has multiple combi valves. Anyway.. hope that help..

 

There will be a combi valve for each bank. So the v engines have two,both at the rear of each head. Checking the lines from the engine to the valves is a great place to look for leaks. Sometimes the valves themselfs do not hold vacuum or are stuck closed. Also look at the pump. When the engine starts cold do you hear the pump kick on. Aneasy way to check the pump is to remove the air inlet hose for it from the air box. Start the engine cold and feel for suction from that hose. If you have suction the pump is moving air. If not you have to check the pump and its electrical wiring for fault. There could also be a leak in the pressure line from the pump to the combi valves.

 

I have a 99 A6 2.8 Quattro with the same problem, This might sound dumb but does anybody know where the secondary air pump is located for this specific model? I read that it was under the headlight on the passanger side but so far I wasn't able to find it.Also when the car is on sometimes I will get a "hissing" soundthat seems to come from under the dash orunder the driversside (I already checked for snakes andthere are not any )I'm thinking most likely both issues are related since that sound might be ahose loosing vaccum but I'm agreen horn so I wanteto ask you guys about it. Has anybody had the same problem? Is there anyvaccum lines under the driversside?Does anybody have a diagram or pictures of what to look for? (I found some diagrams but they were for the A4)I would like toat least know where to look since I haven't been able to do it myself allthat great because it has been sosnowy in Utah and Idon't have access to a garage since the weather seems to be getting nicer I though I would ask and give it a try. I already orderedBentleys service manual but it will take afew days to get here.Thank you in advance.

 

The a4 and the a6 engine compartments are pretty similar. Alot of the parts are the same for the two so the diagram should be somewhat helpfull. I would definatly look for the cause of the hissing. To find your secondary air pump, follow the hose that comes of the front of the airbox. It goes directly to the secondary air pump.

 

I got news from AUDI regarding this issue, it was part of a recall for the secondary vacuum lines, I took it to my dealership today and they fixed it for me, now the check engine light is on, so if your problem are the vacuum lines then it's free, I don't know how many models are included in the recall but mine is a 99 A6 2.8, in the letter I received from AUDI they also said some A4 were included, if this is the wrong place to put this post I apologize I just though I was going to share my experience and maybe somebody else can get their problem fixed for free it doesn't hurt to check with your dealership. Also the way the dealership (Ken Garff in Orem, Utah)took care of my car was awesome they had 4 different recalls and it only took them 4 hours to have everything completed.