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Maybe two problems?
1. Gas smell when idling. Not all the time, on and off. I lifted the back seat and didnt smell or see anything. I don't visually see anything in the engine compartment. Also gas smell in oil. Looks a bit thin.
2. I have a check engine light. P0441, incorrect purge flow. The dealer replaced the purge flow valve a few years back. Since then the light would come on, stay on, and then shut off for a period (I would run it over to get smogged when the light went off).
I tested all vacuum lines I could reach for leaks with propane and didn't find anything. Gas cap replaced. For a minute the light went off right after new gas cap, but went back on and has been on since. Tried low fuel in tank, middle level, and full. No difference.
Performance is perfect. Starts fast, no rough idle, no misfire or stutter. I do hear slight knock when listening closely.
I'd start with looking at the fuel trims to see if it's an engine related fueling issue. If they look OK, then focus on the injectors - you might have one stuck open. See what your scan tool will give you in terms of injector firing patterns.
After that I'd be focussing on the fuel vapour setup. You said the purge valve had been changed - what about the cannister? Possible that its reached the end of its life andbits clogged - That alone will upset the purge valve and might account for your fault code.
Last edited by BlackML550; Mar 12, 2025 at 03:51 AM.
That’s me in the other thread. I’m still inconclusive on if my issue is resolved on my C250 M271 fuel smell. It will take several months to see if the smell comes back. (I had an injector replaced).
can crankcase vent system clog cause P0441 or 451?
I have been replacing parts to clear this p0441 and p0451 and not getting anywhere. Is it possible that if my crankcase breather system is faulty (oil dilution issue I have) that the 441 and 451 codes may be directly related to that issue? How do I go about testing the breather system? Is that just removal or can it be tested on vehicle?
Regarding the crankcase vent system, would my oil cap bounce around at ilde when unscrewed if it is that problem? I took a video of it too and attached it.
IIRC, P0441 & P0451 refer to the evaporative emission system for fuel tank vapors. Was the fuel tank pressure sensor also replaced? Look for a deteriorated piece of tubing or a cracked connector. Also examine the canister carefully at the mounting points. That’s where mine cracked and it was almost invisible.
The bouncing oil fill cap may also indicate that the low side of the crankcase vent system is insufficient. That leads to the rusty dipstick, but I don’t think it’s directly related to the codes.
Hi, I removed the low side crankcase breather assembly and don't see anything wrong from what I can tell. Is there a way I can test the Bleeder now that its off? I just cant keep spending hundreds at a time for parts just to see if thats the problem so if theres any way to test it I would greatly appreciate the advice. I bought a new breather hose check valve and compared it to the one on there and they both respond the same to blowing into them. I have it so ill swap it anyway, but the only other part on there is the Bleeder (the piece that bolts onto the case) all of the hoses are in perfect shape.
Visual inspection and blowing to test check valves is all I know about that system and yours looks good. Mine wasn’t. The check valves were gummed up and not functioning. I would put it back together and send the new part back for a refund.
If your fuel vapor purge system is also okay, then it’s hard to know what is triggering the codes.
the vent valve seams ok, blows through the same (flows one way, blocks other way) as the new vent valve (small valve with the arrow). The valve I circled, the part that bolts to the crankcase, I cant blow through either direction. Should I be able to blow through that part in one of the directions, or could that be my blockage? Is that part itself repairable/cleanable?
(the codes are another issue, I was just wondering if they could be thrown if there was a crankcase ventilation problem. I do have diluted oil, rusted dipstick, and oil leaking.)
the vent valve seams ok, blows through the same (flows one way, blocks other way) as the new vent valve (small valve with the arrow). The valve I circled, the part that bolts to the crankcase, I cant blow through either direction. Should I be able to blow through that part in one of the directions, or could that be my blockage? Is that part itself repairable/cleanable?
(the codes are another issue, I was just wondering if they could be thrown if there was a crankcase ventilation problem. I do have diluted oil, rusted dipstick, and oil leaking.)
Your symptoms are the same as mine. I think you’re supposed to be able to blow through it in both directions with some resistance, but to be honest, I didn’t get that far because mine had a broken vacuum line on the check valve and the lines were plugged with sludge. I just replaced the whole thing. You may be able to clean it in gasoline. It’s plastic, so I think carb cleaner would destroy it.
But that didn’t get rid of the codes. Sometimes I had the small leak, others the large leak - gas cap off warnings. I took the car to a local indie MB shop and the owner, who I know well, found the cracked evaporative canister. The crack was invisible unless you moved the canister with your hand. I gave him a few $$ for diagnosis and changed it myself with a used one from eBay.
Ok so I pulled the crankcase breather assembly and the check valve was fine but the bleeder valve was clogged. Hoses were in great shape, no leaks or clogs. I was able to order that exact bleeder valve, genuine mercedes, for $40 without having to buy the entire assembly ($200+) --photos below, which include the part number (only need to pop the metal ring out of the base so the other hose fits back on--see photo). For anyone interested, the new part you can blow air from engine side outward, not the other way, and there is a bit of resistance just like the check valve. There is also a really great post about why that check valve sucks so bad and a modification that I will link, but that was beyond my interest at this point, however,I may look into that down the road.
I put it back together and while engine cold, theres vacuum at the oil cap. When warm, cap bounces. I know the bleeder was clogged so I am glad to have that replaced. I have a valve cover on the way and will just do that too. Will see what happens after that.
Still have the 441 code and now the 2422 is back (I checked the ohms on the canister check valve to make sure that didnt go bad in the few days its been on but it checked out good) so I ordered the on tank pressure sensor and when it arrives I will lower the tank and replace it. I also took the canister off again and thoroughly inspected it. Nothing rattles when I shake it, no visible cracks, no clogs, and I capped and blocked outlets and pushed air in, seamed to hold good.
Unfortunately now I am getting a random all 4 cylinders misfire (it runs and idles beautifully), so I sprayed maf fluid all over the throttle body and intake manifold, actually everywhere a leak is possible, and got no indication of a leak (new intake manifold gaskets and new throttle body gaskets).
@TimC300 Yes I just replaced the old canister shut off valve with a new genuine mercedes one about 3 or 4 weeks ago. A few days ago, I took the new one off (after getting the 2422 code again) to check the ohms and it read the same as before I installed it. I also thoroughly checked the canister and just couldn't find anything wrong with it. As soon as I can afford a Sentry I will get it, but for now I am just trying to get by. I saw a post where a mechanic who got the same codes was able to use sentry to determine that the issue indeed was the on tank fuel pressure sensor (sending bad info). So that part is on its way and when it arrives I will get it on jack stands and lower the tank to replace it.
On the PCV blow-by issue, I replaced the low side check valve,and bleed valve (which was clogged), and made sure the other hoses were in perfect shape. That repair did not stop the oil cap from bouncing around, especially when warm, so I got a new valve cover and am in the process of putting that on right now. There was oil leaking into one of the spark plug inlets so I guess it was needed anyway.
*During the cleaning of where the vavle cove fits on, I very lightly brushed against the plastic timing chain guide with the rag and the little pegs that lock it on, broke off and fell in. I cannot believe how brittle and fragile those are. Now I have to flush them out, another headache to add Hopefully I can find them in the oil pan or in oil when I drain it all out. I just cant get a break...
Update: Replaced Valve Cover and timing chain guides
Blowby issue: Ok Valve cover has been replaced. Cylinder 1 plug/cop was almost full of oil and I found a few other spots where oil was leaking from the valve cover, so I am glad I opted to replaced it. However, the oil cap still dances--video attached. I don't see much difference in the way the oil cap bounces after replacing the lower breather parts, and the valve cover, so I have no idea if my problem is solved. Will take a little time to see if the oil continues to get diluted.
Timing chain Guide pegs that fell in: I sucked out the oil, strained it, no pegs, so I removed the drain plug and put a pan down and poured 5 quarts of oil down the timing chain area so it would would maybe flush the little pegs out the drain. I did that a couple times but didnt get the little plastic timing chain guide pegs. Im hoping they will get caught up in the drain pan. Since this happened I have been rewatching all of the valve cover job videos online and have been noticing broken pegs!!!--I added a snapshot from one of them below.
I also found a lot of oil leaking from the Turbo Line. Theres a thread on a fix for that that I will try out. Pics of that included below.
Update: On the rough Idle and four cylinders misfire issue, it was the Swirl Flap Position. The swirl flaps moved when I cleaned the intake manifold (I removed the swirl flap motor when I took off the intake manifold, to replace the lower pcv). I removed the swirl flap motor today and reset the position and it runs smooth, no more misfire.
The fault codes p0441 and 2422 have not come back and I am hoping they won't since replacing the on tank fuel pressure sensor. Fingers crossed. Also looks like oil leaks were dealt when the valve cover was replaced. Again fingers crossed.
Thanks everyone for all the advice and I will update again in a bit.
For what it's worth I've replaced the breather components and valve cover on my c250 and I still have a little filler cap bounce. I've also compared a handful of M271 Evos on dealer lots and they all have bouncing filler caps. I've decided to leave mine alone as there is no associated problem it seems.
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(I checked the ohms on the canister check valve to make sure that didnt go bad in the few days its been on but it checked out good) so I ordered the on tank pressure sensor and when it arrives I will lower the tank and replace it. I also took the canister off again and thoroughly inspected it. Nothing rattles when I shake it, no visible cracks, no clogs, and I capped and blocked outlets and pushed air in, seamed to hold good.
Hopefully I can find them in the oil pan or in oil when I drain it all out. I just cant get a break... 
