Egr codes appearing. Possibly a vacuum issue?

[mike ryan]

I have an allroad c5 2004 2.5tdi. I have had a couple of issues where my Mil comes on and the code indicates an egr insufficient flow error. I have cleaned the egr valve. Not that it was dirty really, and used a vacuum generator to test the diaphragm. All seems OK. The light reappeared on the way home today so that hasn't cured it. I had wondered whether the vacuum pumps deteriorate on these engines. Should I be checking it. If so what pressures make for a good or bad pump. This also had me wondering if the check valves in the vacuum connection to the servo ever fail. I need to replace mine anyway as I broke off one of the nipples where the small hose attached. I have looked at elsawin but I can't see a procedure for testing any of the vacuum system.

Any body else had similar issues?

Thanks Mike

[amiram]

If there is a problem with the vacuum pump then the brake pedal will be very hard to stop and the turbo cannot provide the necessary pressure either.
Check out the N18 (the EGR Operator) and Vacuum Tubes

[Crasher]

I would suspect the solenoid if there are no vacuum leaks.

[mike ryan]

I am back for an update. The p0401 egr insufficient flow fault has reappeared on a daily basis. The Mil only comes on part way through my journey rather than at start up. I am living with it as the car is going great other than the mil being on. It does annoy me so I want to get to the bottom of it.

What I tried so far is going through the whole vacuum system for leaks. I replaced any o rings, changed the small hose with new stuff and used cable ties on any elbows and joints I couldn't replace. This didnt fix my issue but has significantly improved the power and smoothness of the car.
I had another second hand egr so swapped that out but it has not solved it either.
I have finally managed to find a solenoid valve and will change that as you suggest. I would rather do some diagnosis instead of just keep changing parts. Can I use vcds to measure the egr function? Are there any other indicators of a bad egr valve. Could it be a bad maf that's masked as an egr error?

Cheers


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[Crasher]

VCDS will allow you to cycle the EGR in basic settings 003. Disconnect point 7 and apply a vacuum to the system.

[amiram]

Check the metal pipe connecting the EGR valve and intake manifold PN. 059131525Q Cracked or broken.