Has anybody figured out what causes the code P0456 on 2005 C230

P0456 = Evaporative Emission Control System Leak Detected
(very small leak)

You have an EECS leak. There are many threads in this regard.

Can be anything from a loose filler cap to a cracked filler pipe to a leak in the carbon canister to a purge circuit leak. Cracked filler pipes were common on 2005.

Check the basics. If you can't find it have the system smoke tested.

For my 2005 C230K it was a leaking fuel filler neck - apparently a very common problem with the 05s. Diagnosed with a smoke test from the dealer.

thank you guys
what did you end up replacing on it?

My dealer replaced the fuel filler neck. My car was under warranty at the time with about 35,000 miles. 4 years and 110,000 miles later the code had never returned.

Thanks a lot LILBENZ230, i guess it was a defect in the part, thanks to you now i know where to look

thanks Glyn M Ruck i am going to guess its one therse hose that are leaking

Unfortunately usually the metal filler pipe on 2005.

if its the metal filler pipe there will be no option but to replace the entire unit i guess
i will check it before ordering the new one

Please check it. It could be any joint/union.

I had the same code. It was very annoying. I Couldn't pass smog. I initially changed the gas cap and purge valve. The check engine light came back on several days after resetting all the codes to cycle I eventually went to get a smoke test done ($75) and smoke was coming from the fuel filler neck region. I replaced the fuel filler neck and that solved my problem. I really wanted to thank this forum informing us the common problems on our vehicles and I wanted to share my story. I spent over $750 on parts and labor and over 2 weeks trying to correctly diagnose this problem with the help of a Mercedes tech friend that I have. I really don't know how much this would cost thru the dealership, but it might be exoensive unless you do it yourself.

I had the exact same problem on my 2005 coupe. The dealership changed my MAF filter and then informed me they wanted $670+ to fix the leaking evap system.
I tok my car to my indy mechanic who was able to place a "stent" to repair the broken hose. Cost me $90.00. That was about 4 years ago and it's still holding. But the key is to run the smoke test. That will tell you where the leak is. Be sure to remove the right rear fender liner because that's where the charcoal canister is.
I hope this helps, Doug

Oh,and I forgot to say that living in Canada, sometimes snow gets caught up in the upper fender, then you hit a pothole (none of those in Ontario, right) and break the hose. Anyway that's what happened to me and I thought I would pass that along to you. Oh and Glyn M Ruck is a genius.
Good luck Doug