Robjr

All.....

Any MB tech's on line right now? If so, here's my question:

I've had a CEL with a DTC P0446 (Evap Shut Off Valve) now for about 5 months. Here's what I've done:

1. Installed new purge valve
2. Installed new shut-off valve with new pigtail adapter.
3. Check continuity on every fuse, relay in front SAM and all the way back to new shut-off valve. All good. Just in case, I've replaced Circuit 87 relay (K) and Relay I in the front SAM just for fun.
4. Installed new sending unit in late 2022 due to cracks on top of sending unit. Also checked top of fuel pump and found a couple of cracks that were repaired with JB Weld Marine and all's good there. No fuel leaks for sending unit/fuel pump.
5. Completed smoke test for evap line from purge valve to evap charcoal canister, including new gas cap with good vacuum while engine running. No leaks!
6. My AMG tech at local MB Dealer found that the new pigtail adapter had crossed wires and those were changed but P0446 DTC and CEL still raise their ugly heads, respectively. All Readiness Monitors show "green" after 3 drive cycles.

Any suggestions?

Thanks, in advance, for any assistance that you can share.

Rob

Pedro Sanchez

Hi Rob, question. When they had it at the dealer did they do a fuel tank leak test through the Xentry? It will either close the charcoal canister and have you start the engine and actuate the purge balance to build vacuum in the tank. Or it will close if the charcoal canister and have you use a vacune pump to build vacume in the tank. I think we need to start the diagnosis from scratch again to make sure something wasn’t missed. This should be the first step in the diagnosis.

Robjr

Pedro.....

My C55 and I spent a total of 4.5 hours in the bay with the Merc tech which resulted in finding a bad pigtail connector that he re-wired correctly. He pulled vacuum test (2 millibars psi). As I previously stated, there were fuel tanks leaks due to cracks at the tops of the fuel pump/fuel sending unit which both were replaced with new units during the 1st week of June 2023.

Three weeks ago, I installed a new front SAM which MB tech re-programmed SAM to recover electronic features specific for my C55. Still getting P0446 DTC/CEL!
I have appointment on July 25th and MB will specifically check continuity for Circuit 87 from front SAM to shut-off valve on charcoal canister.

I'll report results afterwards.

Thanks for the ideas and comments.

Rob

Pedro Sanchez

Ok, keep me posted. Can I ask what dealer your taking it to? Also, by any chance are you having a hard time filling up the car, like does the gas nozzle click off on you?

Robjr

Pedro.......

I've got friends (shop foreman at MB Ontario) and service manager (Walter's MB) who treat me very well with no B.S.

No past issues ever filling up car; however, to eliminate any possible dtc's, I rebuilt the charcoal canister 1 month ago using activated charcoal granules acquired from PetSmart (its the stuff used in the fish filters for aquariums. Simple task using coping saw to separate upper and lower half then emptying old charcoal granules into zip lock bag and weighing on a digital scale (approx. 46 ounces). Cleaned, via air compressor, paper filters at bottom of canister. Used belt sander on separated upper and lower portions of canister to get an even seal. Filled canister with new 46 ounces of activated charcoal granules and sealed upper and lower half with JB Weld Plastic Epoxy and clamped together for 24 hours.

Smoke-tested charcoal canister next day for 10 minutes and no leaks were found. Reinstalled canister.

Rob

Pedro Sanchez

Ok, we’ll what I was wondering is not if the shutt off valve had a leak but if the shutt of valve was stuck closed. Mine would stick closed and cause me to have a hard time filling up. It should vent during normal operation and it’s only closed during a fuel tank leak test to make sure there are no other ways for the vapors to leave the tank. So like when I was testing my car I would be able to close the shut off valve using the Xentry. Then I would be able to pull a vacuum fine because everything was sealed up. But then when actuating the shut off valve open you should see vacuum immediately drop but on mine it would slowly drop showing a sticking valve. The other thing I can think of is checking the line from the engine to wherever it is you hook up the smoke machine. If when the Engine Control module is checking the system and actuating the shut off valve and purge valve and doesn’t see a change in pressure in the tank it’s going to think there is a problem like a leak. But it could be there is a blockage in the line or the purge valve is not actually opening up. There could also be a leak in the line but then you would possibly have running issues. I remember having an issue where the problem was a tear in the elbow connecting the purge valve to the line going to the tank. When I would disconnect the line to hook up the smoke machine I would leave the elbow on the purge valve so I would never be able to find a leak but as soon as everything was put back together it failed. Now that I think of it the engine control module is monitoring the pressure sensor for pressure changes during this process. If you have a bad pressure sensor then of course everything is going to work but the engine control module won’t know because it can’t “see” the change. You should be able to see the pressure sensor actual value during the fuel tank leak test with Xentry.

Robjr

Pedro, Everything has been replaced, I. E. Purge valve shut off valve, 90°, rubber elbows for the purge valve, new pigtail, adapter for shut off valve, rebuilt charcoal canister, new front SAM, new sending unit with pressure sensor and fuel pump, new relays and fuses in front SAM, gas cap, etc. The entire evap system was smoke-tested twice, once by me and once by my MB tech with no leaks either time. I am anxious to see what we will find next week after some more testing with the Xentry system, I.e., fuel tank, leak, etc. Rob

Pedro Sanchez

I’m curious to see what you find as well.

Robjr

All....

Ok.......Evap issue finally solved!!!

Update on what happened while I was in the bay with the MB tech (Service Manager is a personal friend):

"Signal and ground wires on fuel tank pressure sensor were swappedon new electrical adaptor resulting in the purge valve does not flow enough triggering a fault in ME control unit 2012-002 ~ Y58/4 (Activated charcoal canister shut-off valve). Mechanical defect of new component Y58/1 (Purge control valve) is permanently open (P0446). Fault description states this fault sets when a plausibility check fails; check occurs when the fuel tank vacuum is too high with purge valve closed and shut-off valve is open prior to performing a fuel tank leak test. Monitored fuel tank actual value with gas cap removed and engine off, found it is reading -46 hPa when it should be 0 hPa."

"Inspected fuel tank pressure sensor wiring repair and found signal and ground sockets have been swapped. Disassembled connector and swapped socket locations. Verified actual value now reads -0.6 hPa. Well within tolerance of the sensor. Performed fuel tank leak test via Xentry and found test aborts as not enough vacuum is built up quickly enough. Test fit reinstalled original purge valve supplied by client and performed the test again. Found the test now passes with a 1.6 hPa delta with a specified limit of 5.0 hPa. Cleared all fault memory, performed extended road test and found no faults stored in the ME control unit. Recommend client drives vehicle as normal to set emissions monitors prior to upcoming emission test."

In laymen terms: The fuel tank pressure sensor on top of the brand new sending unit has new wiring connections setup. When I installed the new sending unit, I individually cut each of the three (3) wires, one at as time, and spliced them onto their respective corresponding wires thinking the connections were correct. NOT!!!
The new OEM connector bought from MB dealership is the updated connector in which the signal and ground sockets were swapped. At that time, believing the OEM connector was a wired "plug and play" installation, I should've tested each lead for voltage and ground connections! MEA CULPA!

In addition, as I previously stated, the installed new purge valve analyzed by the MB tech was found to be permanently stuck open! Whodathunk!?!?! That's the second new OEM part that was defective (remember the updated EVAP shut off valve pigtail was also crossed-wired) which complicated solving my Evap DTC P0446 CEL!!!
As I always do, I keep all of my uninstalled/removed old electrical parts just in case something like this happens.

As always, MB does not allow returns for any electrical parts unless you can specifically prove to MB they're defective and, for the most part, its not worth your time or effort to go through that B.S.

My personal friend MB Service Manager stated I wouldn't believe the number of defective electrical parts they install on MB's that are found to be defective. This is a direct result that MB factory no longer manufacturers their own parts because they've found that contracted part suppliers can do it cheaper.....HOWEVER, QUALITY DOES SUFFER! End of story....PERIOD!!!

I'm grateful that my friend took good care of me and a round of golf is now in order!!!

Rob

Pedro Sanchez

Good to hear they figured it out! I was kinda hoping to take a crack at it if they didn’t.lol

brauhaus313

Glad to see it worked out for you finally. There were a few things going on here that likely couldn't have been solved with the collective brainstorming of this forum.

On a bit of an unrelated note, you mentioned in another thread that you zip tied your new FSU hoses to your original fuel pump because the hoses of the new FSU were too large for the fittings on your original fuel pump. Is it holding up/functioning normally so far? I have a new FSU waiting to go in but the new OE fuel pump I ordered with the correct fuel return line fittings for the new FSU hoses came with the level arm broken and was told that was the last one in the entire country. If everything is still working fine with the return lines simply zip tied to your original fuel pump, I may just do as you did.

Robjr

brauhaus313....

I, too, am very happy this issue has been resolved! Thanks for your sentiments!

Yes, I needed to zip tie the hoses on the newly installed sending unit to the fuel pump due to their larger hose diameters than the original oem hoses. They held up; however, the top of the original fuel pump finally showed some cracks and I installed a new one about 4 weeks ago.

Give the zip tie hack a try as it did work for me until those cracks appeared.

Good luck and keep the forum posted!

Rob

Robjr

brauhaus313.....

Does the level arm look like the OEM fuel pump's level arm? If so, install it on the new fuel pump.

In case anyone's interested, I have a new fuel sending unit that I installed in April 2023; however, when I was torquing down the large black nut, the torque wrench with the attached large spider wrench slipped off and broke the male intake 90 degree tube that the hose slips onto. If someone is adventurous, the might try to plastic epoxy (JB Weld or other stuff) it back together. Just saying......

Good luck with your fuel pump, brauhaus313....

Rob

brauhaus313

It was the plastic slot fitting holding the level arm in the correct orientation that was broken. Perhaps I could have swapped the plastic arm with the slot but having never done it before, I thought there was a high chance I would have ended up breaking both my original and new fuel pumps trying to do so. Returned the fuel pump the next day so I'm going to go with the zip tie method. AFAIK, our fuel pumps generally last quite a while and my original only has about 54k miles on it. So, I don't mind getting ~$200 back for the broken fuel pump I ordered solely for the new FSU hoses to fit properly.

brauhaus313

Installed the new FSU and zip tied the hoses to the old fuel pump. Seems to be working fine but out of paranoia I think I'll end up installing an updated fuel pump as well. Broke apart my old FSU to see the condition of the filter.


Clearly dirty but not sure if it was to the point where it was hindering performance or overworking the fuel pump. The black residue on the cardboard is what was left of the fuel that dripped out of the FSU and evaporated. The fuel was pretty dark and dirty.