EGR valve Code P0400 - Benzworld.org - Mercedes-Benz Discussion Forum

whistleplaya · 02-23-2010, 07:32 PM

I have a 1999 c280 with about 150k, the P0400 code for the EGR valve still comes on even after the valve has been replaced and the codes cleared. The tube that goes into the manifold has also been taken out and cleaned.

bmeister · 02-23-2010, 08:14 PM

Did you inspect the hose for holes? There is also a MOT that may need cleaning, it should be tapping away when the engine is running. Other thoughts might be the changeover valve not operating. B

wichipong · 02-23-2010, 11:08 PM

i had the same thing... checked the EGR valve and it was ok... turns out to be the changeover valve... i replaced it and it never went back. GL

whistleplaya · 02-24-2010, 12:38 PM

the changeover valve came new with the EGR valve i bought

gmascoli · 02-25-2010, 10:16 AM

bmeister-
Regarding the MOT, I have a '99 C280 with 193k miles. I replace the MOT with a new one a few months back because the old one was NEVER tapping away.

I put the new one in and guess what...it just sits there doing nothing also! I'm guessing there may be an electrical fault? The codes that are thrown don't seem to indicate the MOT having a problem, but I am a bit lost....

Any thoughts on it?

bmeister · 02-25-2010, 03:26 PM

Did you inspect all the fuses and voltage to the MOT. You may have carbon deposits clogging past the EGR pipe into the engine cavity. Some people have used Seafoam with decent results. Pm'd some links concerning carbon build-up. A SDS may have to be done to pull specific codes, obd is just a starting point. B

gmascoli · 02-26-2010, 04:59 AM

bmeister-
Fuses: I'll have to review the Haynes maual I have to see what circuit the MOT is on so I can check the fuse, although I have not come across a blown fuse when I've check in the past.

Voltage: I'll need to pick up a multi-meter and check the voltage across the pins for the MOT connector - any advice on doing this?

Carbon Deposits - how do I check on "carbon deposits clogging past the EGR pipe into the engine cavity"? Also, what do you mean "Pm'd some links concerning carbon build-up"? I'm sorry I'm not more up to date with terms, what is "Pm'd"?

Codes: I can pull all the codes with the OBDII at Autozone - is that adequate? What do you mean "SDS may have to be done"

Again, I appreciate your input and apologize for being less than literate about Pm'd and SDS