backtosand

I have an Audi A4 2.8L showing a P0401 trouble code. Haynes repair manual does not show the location of the EGR valve or the parts immediately around it.

Can anyone help with a picture or a link to an engine diagram? Many thanks.

AudiMick

Only on the 96-97 12 valve V6.

Rear of Bank 2 under the cruise control vacuum tank.

If you are getting an EGR insufficient flow, do not replace the valve.It is the EGR passage between the valve and the manifold that is blocked.

This is a recurring problem with the 12 valve and changing the valve doesn't fix it.

Old Dog

Here is a link to another AudiMick reply dating back to Dec 2008 detailing a little further on what needs to be done plus a bonus pic .

https://www.audiworld.com/forums/sho...d.php?t=349809

You should, in the future, do a search first before asking for help. If you are unsure what is the best way to do a search, I'd be more than happy to help.

Good Luck!

backtosand

Thanks for the assistance. You mention a link but I don't see it. Please repost.

Old Dog

Woops sorry. Must have had a senior's moment . The link is now included where it should have been in the first place.

Take care.

backtosand

Thanks, Old Dog and AudiMick. The info helped greatly.

New question: On the floor of the black plastic air duct behind the throttle body is a 2-inch rubber "flapper valve" that allows recirculated gases to enter the intake manifold under positive pressure (my guess anyway). The mat is torn and non functioning so I removed it. Replacement of the entire duct piece with a new rubber valve is roughly $130. How important is this valve? Any harm if I operate without the piece in place?

Note to other ham-fisted DIY's: You will pay dearly for breaking the plastic hoses that lead into the air duct behind the throttle body, as I have done. They are quite brittle. Replacement cost is more than $120 for each hose!

AudiMick

That valve effectively acts as your PCV , it allows the blow by gases to be vented into the intake , removing the (non return) valve allows air from the intake to be drawn into the crankcase.

I don't know if it will cause a problem. Some people have spliced in regular "autoparts store" PCVs into to the vent lines to maintain the correct pressure relationship. Some have modified the system and gone with a catch can, which is better since it stops the EGR re-blocking up.

Craig Cringston

Does bank 1 valve cover vent our through that tube or does air vent in?

Victorymike18

I just want to make sure we're still talking about the 12v V6 since this thread is pretty old.

On the 12v, both valve covers vent to the base of the black plastic plenum tube (like a goose neck). Everything here happens after the MAF sensor which means it is clean filtered and metered air.

This shows how I found my system, with a disintegrated plastic hose from the Passenger valve cover, and a "replacement" rubber hose on the Driver side:



Here's that one-way flapper inside the plastic plenum, note mine is somewhat damaged. Ignore the moisture, I had been cleaning it:



A view from the rear Passenger side (VC vent hose isn't installed):



And view from the rear Driver side (VC vent hose isn't installed):

desertsage

Hey Victorymike18! Great photos and explanation. This helps me, too.

Was just perusing this EGR port clean-out info in preparation for my head gasket job.

Is the little orange flapper inside the TB plenum the one that acts as a PCV valve? Were you able to repair or replace it?

AudiMick's comments are helpful, especially to the link to the vac system and the Audiboy mod (which I'm not completely understanding). Makes me understand more fully just how important the check valves on top of the TB plenum are.