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2014 Mercedes-Benz C350 4MATIC
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Discussion Starter · #1 · (Edited)
Code P0400

Hi everyone,

I am getting the code P0400. My mechanic suggested to change the EGR valve, and after changing it, I am still getting the same code. Now he is thinking that it could be my catalytic converter... A new cat is quite expensive, so I wanted to see if anyone had any suggestions on what this code could be and/or what is causing this code. Any help would be greatly appreciated. Thanks in advance.
 

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2001 CLK55 AMG, 2002 C32 AMG
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first of all, im assuming that you meant code p0444, since i couldnt find any codes with p4044 lol

hopefully your mechanic checked out your vacuum lines, but i would check for broken or loose or missing vacuum lines. with the engine running, do you hear any hissing when standing at the engine with the hood open? this would indicate a vacuum leak.

also, check your gas tank cap and make sure its tight. after all this, i would recommend resetting the code and see if it returns. if it does return, note how long it takes to return. is it right away, is it after say 3 trips somewhere... ect.

also, if you are handy with tools you can try removing the small vacuum valve and cleaning it out with some spray cleaner. if your interested, let me know and i can show you what needs to be done. i dont know why your mechanic was messing with the egr valve... o well, maybe im missing something.
 

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Discussion Starter · #3 ·
So sorry just realized I typed it in wrong it is actually P0400. Maybe it will be easier to diagnose the problem if I provide the correct code, haha.
 

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ok, well i guess we are dealing with the egr valve then :p haha

i would still recommend checking your vacuum lines. there is a vacuum line that goes to the egr valve and i would trace that all the way back to its source. make sure the line is good, not cracked or loose.

if your vacuum lines check out ok, then i would recommend removing the egr and cleaning the metal pipe that it connects too. this can get blocked with buildup. any carb cleaner spray should be able to blast it out of there.

i dont really anticipate your cat being bad, since none of your o2 sensors are going off.
 

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96' C220
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Reset

I don't mean to be obtuse, but did you reset the Computer after changing the EGR?

Good Luck!:thumbsup:

C as in 220
 

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95 C220
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check your valves first if it is holding vacuum. then check the other end where the vacuum lines connect to the change over valve. that might be the problem as that was throwing my car off. change the changeover valve (its an easy DIY) and it should help you out.. good luck!
 

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check your valves first if it is holding vacuum. then check the other end where the vacuum lines connect to the change over valve. that might be the problem as that was throwing my car off. change the changeover valve (its an easy DIY) and it should help you out.. good luck!
they supposedly changed the egr valve... so hopefully the valve is working properly lol.
 

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Discussion Starter · #8 · (Edited)
ok, well i guess we are dealing with the egr valve then :p haha

i would still recommend checking your vacuum lines. there is a vacuum line that goes to the egr valve and i would trace that all the way back to its source. make sure the line is good, not cracked or loose.

if your vacuum lines check out ok, then i would recommend removing the egr and cleaning the metal pipe that it connects too. this can get blocked with buildup. any carb cleaner spray should be able to blast it out of there.

i dont really anticipate your cat being bad, since none of your o2 sensors are going off.
Hi, I was wondering where other vacuum lines are located, other than the one running from the EGR valve? Also when we changed the EGR valve we cleaned the pipe that was connected to it thoroughly. Also my mechanic did mention that it possibly could be my catalytic converter. He said to take it for my emissions test (Ontario Drive Clean Program) which is due soon, and then said he would be able to give me a more definite answer after reviewing the results. Thanks.
 

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Discussion Starter · #9 · (Edited)
I don't mean to be obtuse, but did you reset the Computer after changing the EGR?

Good Luck!:thumbsup:

C as in 220
Hi there, I was wondering what you meant exactly by "did you reset the Computer after changing the EGR?" Did you mean clearing the error code with a OBDII scanner? If yes, then yes I did do that, and if not, then what do I need to do? Thanks.
 

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Discussion Starter · #10 ·
they supposedly changed the egr valve... so hopefully the valve is working properly lol.
Yes, the EGR valve was changed. I ordered a brand new one from the dealership. Unfortunately, it didn't make a difference and I'm out $250 plus labor :mad:
 

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That's it.

That's what I meant. I wish I had some insight for you. Sometimes you can find similar problems and solutions on other parts of the Forum.

Good Luck!:thumbsup:

C as in 220
 

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try the changeover valve.... i got mine for about 60 bucks plus shipping at parts.com... i just installed it myself... it might be the one that's throwing you off... its your call if you want to spend on it... just an fyi...
 

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if you have a vacuum tester, you can see if there is any vacuum even going to the egr vavle. im not really sure what triggers it to open or close, but if you have more insight on that than i do, you can hook up a vacuum tester and see if its receiving the vacuum when its supposed to. if its not, its most likely the vacuum changeover valve, which i think is located at the front of your engine under the black plastic cover.
 
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