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MB 06 R500; 04 Jag XJR; 02 Maserati Coupe Cambiocorsa
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Discussion Starter #1 (Edited)
2002 Mercedes CLK320. We got a check engine light and we got a code reader to pull the code. The code is P0400 "Exhaust Gas Recirculation Flow". The guy that pulled the code for us says that is the EGR Valve.

The symptom is that when the car first starts to run, the engine idles fine. Once the car warms up, any time you come to a stop, the engine idles roughly and 'surges' or 'pulses'. Far more noticeable when the tranny is in gear as opposed to neutral. Based upon the tachometer, the car is idling at 500 rpm which seems a tad low to me.

Any suggestions or should I go ahead and order an EGR Valve for this thing? Any thoughts or ideas would be helpful.
 

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2003 C240, 2007 ML320 CDI 4matic
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My CEL just came on also...had Auto Zone run a code check and came up P0400 (EGR)! Just funny that i've never had a CEL come before on my 2003 C240 (Base). I had just filled up and overfilled the gas tank and within 30 minutes the CEL comes on. Car runs fine and sounds fine, but hate the CEL being on and can't pass inspection. Any thoughts as to if the overfill could trigger a P0400 code?
 

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'01-E320 & 02-ST2
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31,633 Posts
My CEL just came on also...had Auto Zone run a code check and came up P0400 (EGR)! Just funny that i've never had a CEL come before on my 2003 C240 (Base). I had just filled up and overfilled the gas tank and within 30 minutes the CEL comes on. Car runs fine and sounds fine, but hate the CEL being on and can't pass inspection. Any thoughts as to if the overfill could trigger a P0400 code?
Overfilling the fuel tank is never a good idea, and theoretically it could trigger an EGR-related code (because the EGR and evap systems are tenuously linked), though more often it will trigger an evap code, though sometimes much later. Simply put, it is NEVER recommended to overfill your tank. When the pump clicks off, you're done. If you must go to the next nickel or dime, that's okay, but running it past that runs the risk of trouble.

Now, as to your present issue, how long has it been since you overfilled the tank? Have you erased the code and run the drive cycle to see if they return? (The drive cycle will also speed the readiness of your systems for an emission check.)

I would encourage you to get a basic code reader. Having to run to autozone or elsewhere to take care of simple diagnostic functions is a waste of time and money. And you can buy the little MS309 from Amazon for about $20, which will take care of about 95% of your needs.

If the code returns after clearing and running the drive cycle, you'll have to dig deeper. Removing the EGR valve and tube for cleaning may prove necessary, but first get a length of vacuum line (2' should do it) and then located the vacuum connection on the EGR valve. Disconnect the line (if you break it that's okay, since you have new hose to put on there!) and then connect one end of your 2' section to the nipple on the EGR valve. Then suck on it, build up some vacuum, then put your tongue on the end of the hose to seal it. If it continues to hold vacuum, then you know the diaphragm in the EGR valve is still good. If it won't hold vacuum, then order an EGR valve. (This test is useful because given the labor involved, it would suck -- no pun intended -- to remove the EGR and tube and then find you had to replace the EGR valve.)

If it holds vacuum, the next step would be to remove the EGR valve and tube to clean them thoroughly. Obviously, if you have to replace the EGR valve, you'd want to clean the tube at that time.

Good luck.
 

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2003 C240, 2007 ML320 CDI 4matic
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Thanks Check Codes! It's been a week today since I overfilled the tank. Yes, I cleared code and then it took about 100 miles for CEL to reappear.
 

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'01-E320 & 02-ST2
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Thanks Check Codes! It's been a week today since I overfilled the tank. Yes, I cleared code and then it took about 100 miles for CEL to reappear.
Well, your next step is to read the code. Hopefully it's the same one, but that's the only way to know for sure.
 
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