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Jake, Technician
Category: Audi
Satisfied Customers: 2429
Experience:  Over 30 years experience, 17 years with Audi, Factory trained
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2001 audi a4: obdii..secondary injection incorrect upstream flow

Customer Question

2001 audi a4 1.8t engine. I have obdii code PO411 secondary injection incorrect upstream flow detected, what causes this?
Submitted: 8 years ago.
Category: Audi
Expert:  Jake replied 8 years ago.



Thank You for choosing Just Answer for your query. Yes, I can help you.


P0411 - Secondary Air Injection System incorrect flow detected


The most likely cause would be a split vacuum hose where the hose attaches to the secondary air injection combination valve on the back of the cylinder head, near the top. It is a 2 1/2" shinny aluminum valve with the vacuum line coming in from the left side of the vehicle (your right if you are looking at it from the front). Remove the line cut off the end if it is split and reinstall. Clear the code, you should be good to go.


To get an overview of the systems workings, with th hood open start the vehicle cold first thing in the morning, and allow it to idle. After a few seconds you should hear the air injection pump begin to run. It sounds like a small vacuum cleaner, down in the lower, right front corner. This should be followed by lower pitched thrrrrrr (hard sound to spell) coming from the back of the motor. This is an indication that the combi valve has opened allowing the air to be injected into the exhaust stream. If it is the vacuum hose, the second noise will likely be a hiss coming from the split near the combi-valve. If you wiggle/push on the hose, the hiss may be substituted by the thrrrr sound. If you have the two sounds when running cold, you know the pump is working and the valve is opening.


If you do not have one or both of the sounds, the problem could be a failed pump, pump relay, combi valve activation solinoid, a blocked port in the cylinder head, or possibly another vacuum problem. I would now suggest you bring the vehicle to a Audi/VW specialty shop as diagnosis gets quite a bit more complicated and requires special test equipment.


I hope I have answered your questions and addressed your concerns, should you have any further questions regarding this matter, please do not hesitate to ask. I want you to be 100% satisfied with my answer.


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Thank You!

Jake "The Audi Doctor"