I'm up for emissions and the damn check engine light came on. I cleared it and took it in (worked in the past) but they did actually hook it up to the scanner and wouldn't let me pass until all the checks were performed. It's taken almost 2 weeks and over 200 miles for everything to clear out, but then I got the P0456 code.

Searching shows the filler neck is a common problem, but it seems almost exclusive to the '05s. Wondering if any earlier models have since had this problem?

Also see the DIY for the filler neck is missing it's pictures. Anybody have a copy they can post?

 

Glyn?

 

i had the exact same issue as you on my 2005 C230 after i replaced the filler neck, P0456 has not returned.

 

Thanks Preet! I've seen it reported on lots of '05's, but not the earlier ones. I have a gas cap on the way and instead of paying the $180. for a smoke test bought myself a smoke tester off EBay for ~$100. A smoke machine will come in handy for other vehicles too. Now if I can find the evap system diagrams Glyn posted again I think I might be in business.

 

I apologize to the forum for creating a second thread on this - I should have updated on this thread...

I did get a new gas cap but still throw the P0456 code, so it's time to do the smoke test. Researching on the forum, it seems it could be a number of things - purge valve, charcoal canister, fuel filler neck. I'd like to verify what is the problem instead of just throwing parts at it, especially because the fuel filler neck is ~$500.

Does anyone have the evap test procedure they can post for me?

 

Most other cars I've worked on have a schrader valve in the evap system somewhere for you to inject smoke for the smoke test. I can't seem to find one on the m271. Can someone clue me in?

Or is there an adapter for the filler cap or somewhere else I need to get to perform the test?

 

Got the p0456 on my 05 as well...the only CEL I've ever gotten. Changed the filler neck thingy, no more CEL. It's a pricey part, and there seems to be no shortcuts around it. This was the single most expensive part I had purchased for this car, and still is. Easy DIY.

 

UPDATE: I did buy one of the EBay smoke testers and pulled apart the hoses at the purge control valve to inject the smoke. First tested the hose going to the engine (manifold I assume) and saw no smoke. Then tested the purge valve by putting my finger over the hose going to the manifold and blowing into the other side - couldn't blow any air through. Then hooked up the smoker to the line going back to the gas tank and within a minute saw smoke coming out by the right rear fender well. I was just sitting down to order the filler neck assy, but since it's Saturday and it wouldn't go out until Monday anyways might pull the fender liner out tomorrow morning and see if it's coming out of a rubber hose which could be replaced or the metal pipe itself. Hate to shell out the $500 on a new filler pipe assembly if it's just a hose that can be replaced...

Mercedes Master Glyn couldn't find a smoke test procedure, so I'll try to remember to take some pic's and post a quick write up.

 

OK, glad I pulled the fender liner to take a look (well, kind of glad as it still may be the filler neck too...). The smoke does not appear to be coming from the filler neck assembly, but from an outlet w/hose barbs that appears to go nowhere. Part # is A 000 476 83 32 which search returns as a 'vapor canister purge solenoid'. I assume the outlet is not supposed to be connected to anything and this is the vent?

Big question is: if I'm smoke testing with the engine off, should anything be coming out of this vent, or should it be sealed?

Also, my charcoal canister doesn't look anything like what's shown in the manuals. I'm assuming the big box this valve is attached to and sitting on top of is the charcoal canister?

 

Here are some more pics and the testing setup I've used.

- first pic is smoke coming out of what I believe is the vent on the vapor canister purge solenoid
- second is a pic of the filler neck assembly
- next is the EBay smoke tester, hooks up to the car battery and an air source
- next is the overall setup used
- then a close up of where I injected the smoke. I disconnected the hard line from the *tank* side of the purge control valve (PCV), hooked a small hose to it and injected the smoke into the hose.

 

More update: After more searching around the 'net on this and charcoal canisters/canister purge valves (not to be confused with the Purge Control Valve in the engine bay - there is some confusion on the 'net and even from some parts vendors), I came to the conclusion the big box is indeed the charcoal canister. You can get it out by giving it a good bump from the bottom in the upwards direction as it's just clipped in. I would disconnect the connector first, which was a bit of a bear for me - a reminder here not to pull on the wires. then bump it out, then remove the top hose, and lastly the bottom hose.

From what I've found on the net, it appears the valve IS OPEN with the car off/no power to the valve. Take this with a grain of salt, as I'm not 100% positive...

I checked for power on the car side of the connector. I'm a geek so had a small resistor handy I could poke into the connector and hold a multimeter to. This also let me know which side was positive. I did find power at the connector with the car turned on (Key On Engine Off), so all good there.

With the canister assy out, I figured out how to get the vent valve out - it twists counter-clockwise ~1/8 turn and is held in tight with a rubber gasket. From the earlier test I knew which terminal on the connector was positive, so carefully put some *insulated* (so they don't short) connectors/clips on the terminals and applied +12 volts and could hear the plunger work back and forth. This means the valve is operating and not stuck. BUT, it could still be leaking.

So my initial thought was to put everything back together and smoke test again with Key On Engine Off - thinking if there's +12v with the key on, the valve should be closed and no smoke if operating correctly. I set everything up and smoke tested again with engine off and saw smoke as before. Then went and turned the key to on, went back to take a look and still see smoke, but appears to be less. Hmmmm...... Still inconclusive in my mind because the computer could be holding it in a semi-open state, or I might not have the connector seated all the way, even though I triple checked - tight connection.

Sooo, I took the vent valve back out, hooked it up to +12v and tried blowing into the vent and it's tight as can be.

If this valve is good, the only thing left (assuming there's not a clogged hose somewhere) would be the pressure sensor, which Mercedes notes does go bad sometimes (they say it may stick in a way which sends out a good value but is stuck and doesn't change).

Would still like to hear from Glyn or anyone else who knows for certain, if the valve should be closed with the key on engine off.

Thinking about getting a fuel tank pressure sensor...

 

Yea, it would appear the problem is solved. I was putting everything back together the other night after checking on the fuel tank pressure sensor (which is part of the level sensor assy and is like $300 used on EBay!!! Plus you get to mess with opening up the fuel tank and dealing with all that...) when I decided to electrically check the PCV valve in the engine bay. With no power applied it held vacuum for more than 5 minutes so all good there. I put the little rubber 90 degree hoses back on and decided to blow thru those just for grins and sure enough the hose on the tank side of the PCV wouldn't hold air. Upon closer examination, it had a tiny tear right where those damn click-r hose clamps have the funny loops opposite the clamp mechanism. ~$5 from getmercedesparts.com. In the meantime while waiting for the hose I decided to use some gorilla tape along with the clamp to try to seal the hose. I reset the codes, and when I got home tonight the only emissions ready indicator is the EVAP test! EVAP was the only test that *wouldn't* complete before, along with throwing P0456. This means no more P0456 code and hopefully, knock on wood, all I have to do is drive around for a few days to get the remaining emissions indicators ready. On to the smog test and get my tags...

 

I have been getting P0456s for a while. I had tried a new filler cap to no avail so I finally replaced the fuel filler neck (I didn't know a smoke test was such a simple thing). It went in all right but one poster (I couldn't find his post) said it took him about an hour. Well, he's a better man than I am, but it wasn't too bad. Next, I get to find out if that fixed the problem.

Before I installed the filler neck, I talked to a guy at a shop near buy. He said if you keep the tank above 85% full while you drive it around for a few days, you should pass emissions (at least in NC). If I had known that, I would have tried it but if you don't get your inspection during the proper window, it costs $250 to get it later! Anyway I thought I'd share that. That may get somebody through an inspection on the cheap allow time to get the problem properly fixed . I just think it's more than a little nuts that a person has to spend over $400 (if it's a DIY) to fix a vapor leak that is VERY SMALL!!!

 

mtnman82, nice work.
" it had a tiny tear right where those damn click-r hose clamps have the funny loops opposite the clamp mechanism. ~$5 from getmercedesparts.com" Was it the hose that was only $5 and do you have specifics on what needed to be ordered?
Is that a hose that usually comes new when you purchase the assembly? I'm assuming if this is such a common problem, it's got to be the same hose that fails. but assuming gets me into trouble alot :-)

 

For posterity sake I wanted to follow up on this. The little 90 degree hose came in while I was waiting for the other codes to cycle and clear so I replaced it. I had to disconnect the battery that for something else (can't recall what at the moment), so was had to drive around for the emissions tests to run their course. All the tests had cycled thru when my smog appointment had come up except the EVAP test. The shop said that was the only test that could still be pending and they would pass me if everything else was good so I went ahead and did it so I could get my tags.

Well sure enough, eventually the P0456 did come back. I gave up and bought a new fuel filler neck assembly out of frustration. That seems to have taken care of the EVAP issue once and for all. I still haven't gotten all tests to clear, but now it's the 'HTR' test that is pending after quite a few tanks of gas. I had the 'CAT' test pending for a long time too, but I only drive about 3 miles to work in the morning, am parked all day and then drive 3 miles back home. I took the car out on a longer drive this weekend, doing the '60 mph for 10 minutes, slow down to a stop and idle in D for 2 minutes, then 65 mph for 5 minutes' drive cycle which seemed to work before to clear all the tests and did clear the 'CAT' test but the 'HTR' test is still pending.

I believe the 'HTR' test is the O2 sensor heater? Maybe it's time to replace the 02 sensor, which probably wouldn't hurt since the car has over 105K miles on it. What a pain in the a$$. Damn CA emissions ****'s. At least I have some time and can work on this at my own pace instead of being stressed to get it done and needing the tags...

 

This is SO helpful! I have an '03 E320 and just getting the same message (already replaced gas cap last year). Any way to show a picture of where the valve is in the engine bay? Hoping it's not the filler neck and would like to try this first.