Ckplaner77

Need help locating the fuse/relay for the secondary air pumps. 2005 w12 d3. Any help would be greatly appreciated

MP4.2+6.0

Not sure where it is, but have you tested for power at the pumps right at start up? Or alternately, spin pumps up either with VCDS or by jumping power to them once you pul the connection.

That is, from personal experience one of my W12 pumps ate water and no longer worked. I had secondary air injection codes, but only by conventional diagnostic techniques did I eventually find the bad air pump. They are difficult enough to pull that it makes a lot more sense to jumper power to them, or test the connectors for them (only when motor cold) for power.

Ckplaner77

I pulled out the two pumps and bench tested them. Both run real strong. I am getting a po491 code right at 60-70 miles after resetting the monitors.

MP4.2+6.0

Given that code, you can isolate it to US passenger side. Indirectly that sort of tells you the other side is working since your code is only one side...unless you have more codes? You can check for power at the connector at start up for the passenger side to eliminate the power supply type issues. The pumps are only powered for a minute or so after first start, hence needing to check for power then. With VCDS you can also activate them directly to test electrically. After that I would suspect combi valve for that side, or maybe the air connection to or from that side's pump. You get the code after that kind of miles delay because it takes two cold-hot-cold driving cycles for it to self test and decide there is an issue.

PaulW

I would also look at the vacuum lines going to the combi valves.

MP4.2+6.0

W12's don't use vacuum lines to the combi valves. 4.2's do--or at least my C5 4.2 did--and then are the most likely failure point. Not sure on S8's.

dvs_dave

Very likely a combi valve problem. The diaphragm inside them deteriorates and leaks. Easiest way to test is to hook up a hand vacuum pump to the vacuum lines and see if it holds a vacuum. If it does, then can you hear the valve open? If no to either, it’s a bad valve and/or the vacuum lines running to it.

PaulW

The V10 uses vacuum lines on the combi valves....very similar setup to you C5 4.2 and the D2's.

Here is a post with my issue....but different code:

https://forums.quattroworld.com/a8d3/msgs/13665.phtml

Ckplaner77

Alright I will replace the combi-valve. Thanks everyone for the advice.