Quick question here, wasn't able to find the answer in any other posts. Anyways, I am working on addressing a 17831 P1423 Secondary Air Injection - Insufficient Flow code. 2.8 ATQ engine. Starting with the vacuum lines and breather tube. I have a a vacuum hose diagram and trying to locate all the parts. The diagram shows the vacuum reservoir at the left front of the engine. In my 98 Avant quattro it's there, but don't see one in the 2000 A6 Avant. There was front end damage that wasn't repaired correctly and am wondering if it wasn't replaced? I have found a vacuum line that comes across the left side of the cylinder head toward the front left end near the washer fluid reservoir. There's a section of hose missing, which I will replace; the downstream side goes into a cluster of wires and can't figure out where it goes from there. My hunch is that there should be a vacuum reservoir, but can't find one. I'v attached a couple of pictures and the vacuum diagram I have. Would appreciate any advice!
Attached Images

 

Those ends of the line should be contiguous. And yes, there should be a reservoir down there somewhere. I personally have not seen the location of the vacuum reservoir; however, I had to splice that line before. So I know that it should be there.

 

Thanks for the reply. Right now the line is going to the upper part of the fender above the wheel well. I'll probably pull the drivers front splash guard and see if I can track the line to the reservoir. I have a feeling that it is supposed to be near the front bumper. There's a big open space there and that is where it is located on my 98 A4 Avant 2.8L.

 

This would apparently be what you're looking for/lacking.

Here's an interesting Q/A topic, although for a different engine (4.2l)

 

Thanks Chefro. That's exactly what I thought was missing and already had that item on my watch list on Ebay! I did a little more recon on the car tonight and still can't figure out where the hose that should end on this little blue bottle is going. Right now it is going over the front drivers wheel well and can't track it after that. I think it may just dead end. Tried blowing into it and it is air tight, but minimal volume. I'll pick up one of these blue beauties and see if it helps. Thanks again.

 

Kevin, look up in the diagram since you have it.
From the vacuum reservoir it goes to a T that runs into one of those vacuum valves. If you locate the nearest one to the fuel pressure regulator then that's where your hose should go.
I have a different engine, otherwise I could tell you exactly what goes where, or what those vacuum valves are (for).
In my C4 beside the Charcoal canister that's "burried" behind the wheel well liner - passenger side, there's no vacuum routing through the wheel wells.
There's a chance that the valve the hose goes to, pictured in the diagram, may even be behind the firewall.
As I said, I don't have a quattro and never have seen the engine bay of one. However, that hose either goes alongside the coolant line - close by the ABS module, or under/on the side of the intake manifold.
Has the car a rebuilt title?
I can't picture why the car would be missing the vacuum reservoir.

 

Car does not have a re-built title, but there was apparently front end damage before I bought it. Long and painfull story about the purchase, but I ended up getting the car basically for free. That said, there was front end damage that was not even close to being put back together correctly. Maybe it should have been salvaged, but I am now trying to put back together, the rest of the body, interior and electronics are in great shape. Because of the accident, I've been piecing together unconnected cables, finding cut wires, etc. That's why it's no surprise that a piece like this vacuum reservoir that sits near the front bumper is missing. Assuming it was damaged and not replaced. A little speculation here, but it's the only thing that makes sense right now. I just want to make sure I get everything connected correctly. These forums and posts like yours have been much more valuable than the Bentley Manual I bought.

 

I wouldn't blame you for not passing on a great deal and trying to make the car whole again.
Would bet on the fact that as more fellow C5 owners read your thread will chime in with specific engine bay information. I would gladly provide you with more insight, but the C5 is out of my league. (My Bentley manual is just for the C4)

 

Did some more poking around this evening and finally pulled the front drivers side fender spash shield. Guess what I found, that lovely blue snowman vacuum reservoir. A little surprised to find it there but I guess the vacuum line going into the fender well had a real place to go. I really expected it up front beneath the washer fluid reservoir like it is on my 98 A4 Avant. Oh well, I guess I shouldn't have bought the used one on Ebay today... Hopefully this may help any other A6 Avant owners locate this part, I'll try to post other pictures as I address other parts of the secondary air injection system, vacuum lines.