What is an EGR Flow Malfunction?
 

Got my CE light checked and following code came up on the screen:

P0400 - EGR Flow Malfunction

I cleared the light but am worried it could be something serious so if any of you know then I'd like to thank you ahead of time for your help.

You most likely have a plugged EGR tube

Do a search on "egr tube"
Common on that engine

if this is on your 96 e320 with the m104 engine you'll find this thread interesting:

http://www.peachparts.com/shopforum/showthread.php?t=109372&highlight=EGR+spare

i had a heckuva time getting the thing out and eventually gave up and just cleaned the dirty/plugged side. Problem free since june (4k miles)

EGR flow malfunction means; if the EGR is turned on then the extra fuel/air that comes into the engine SHOULD change the mixture & that changes the intake manifold vacuum! THAT vacuum change is monitored by a MAP sensor, IF the MAP sensor doesn't report the correct change durning that test then after only failed test the check engine lamp will come on the next time the engine is started!

The upper part of the intake must come off to replace that EGR tube!

That is a 2-2.5hr job for expert MB technician, would allow 3-4 hrs for DIYer.

Required parts should run $150.

Be sure to mention that to Gilly! He claimed (in that other thread) that the intake didn't need to come off and likened removing the EGR tube (on the m104) to removing the spare tire...'you sort of unbolt it and it pops right off'

In hind sight I should have just taken the upper intake off instead of screwing around with the damn tube for 3 hours.