C55 AMG Members....

I've owned my C55 since mid-2006 and experienced very few mechanical issues over these years. However, since mid-2022, two DTC's involving the fuel tank sending unit and P0446 Evap Canister Shut Off Valve.
Here's what I've done so far:

1. Installed new OEM purge valve which tested as functioning.
2. Installed new OEM evap shut off valve which tested as functioning.
3. Installed new OEM fuel tank sending unit which cleared DTC.
4. Installed new OEM gas cap.

Here's the list of testing I've completed to eliminate any P0446 potential causes.

1. Completed smoke test for leaks on purge valve; shut off valve and gas cap & tank filler neck. No smoke leaks found!
2. Using multi-meter completed testing for power continuity on the wire circuit from front SAM unit to Evap shut off value which resulted in 12v.
3. Removed Evap Charcoal Canister and completed air flow test resulting in good functionality.
4. Tested for continuity Front SAM Fuse 54 for continuity. Fuse & empty fuse circuit tested good continuity.
5. Tested for continuity on front SAM Circuit 87 relay with audible "click". Relay tested as good.
6. Tested front SAM for continuity after individually pulling each fuse or relay one at a time for each empty "slot", all resulting in 12v. So SAM empty fuse circuits and empty relay circuits are good.
7. Tested all fuses and relays for continuity. All good.

Finally, a friend of mine who's a 20+ year MB dealership AMG tech scanned the ECM with Xentry (?) at his dealership (workshop closed on Sundays thank goodness) and the screen-shot showed the following potential trouble issues:


I've completed the test on those items and, consequently, I'm at a loss for a solution.
A few friends have suggested replacing the front SAM but I don't see the reasoning since every fuse and relay and their respective empty circuit slots were tested for continuity and the results were good.
I also removed the rear SAM and completed the same continuity testing on all fuses and relays as well as their individual empty circuit slots with good continuity, too.

Although I'm not a professional mechanic, I've accumulated a lot of tools, diagnostic tools, and experience over the last 50+ years, i.e., rebuilt some engines, trannys, electrical parts, and all of the normal mechanical repairs from the front end to the rear end (lol) on my domestic cars, Lotuses (1967 S1 Europa, 1974 Europa Twin Cam Special, BMW's, Mercedes Benz, etc., and all of my cars have been very well-maintained with regular servicing (both dealer & me) and were always very roadworthy and, when sold, got top dollar for my efforts

This P0446 DTC issue has been perplexing to say the least and, hopefully, I'll get a little help from my fellow C55 AMG MBWorld forum members.

Thanks, in advance, for any thoughts you can share with me.....

Here's a few pics of my C55.....

Rob


I fabricated the CF Canards a few years ago. Try to get a MB World group buy but less than 10 members were interested. Want to try again? Also, updated front grill as well as all badges with PlastiDip in the Petronas F1 color.

Profile with vented side skirt upgrade.

Profile with vented side skirt upgrade.


Installed a few nice CF dash, console & door upgrades, including flat-bottom alacantra leather steering wheel.

 

You cleared codes and P0446 keeps coming back?

 

brauhaus313......

Yes......My Innova 3160e clears both the regular DTC's but also the MB Enhanced DTC's, too.

Rob

 

When you stated you checked for continuity at the SAM, are you saying you tested for continuity across the female fuse contacts or you tested for continuity from the N3/10 to the SAM?

Just as a matter of course I would check for corrosion, frayed, or misshapen electrical connectors at the Y58/4, and since it seems fuel sending unit code popped up around the same time, the electrical connector to the fuel tank pressure sensor integrated into the FSU.

 

brauhaus313....

While replacing the OEM evap shut off valve, I had to buy a new pigtail adaptor to connect to the oem wiring. After installation of new pigtail connected to OEM wiring, then connected to new OEM shut off valve, I checked continuity from SAM to shut off valve which tested good. For example, using my multi-meter, i checked continuity between an empty fuse in the N10/1 SAM with the front (closest to front bumper) existing exposed-wire plug-in module in the N3/10 and continuity was good.

Yes, I removed Fuse 54, inserted a metal paperclip end into each female slot, attached an alligator clip onto each paperclip and the multi-meter probe and continuity was good. I did that for all fuses and relays in the SAM. Perplexing, yes?

Rob

 

Yes, it is.

I hope I don't sound like an idiot, but to clarify, you tested for air flow through the inlet and outlet of the charcoal canister as well as flow front the vent line from the canister to the purge valve?

 

brauhaus313.......

Yes....smoke-tested from the east side (closest to the front bumper) of the new purge valve all the way to the end of that rubber hose that fits over the top side tube of the charcoal canister......then I removed the charcoal canister and air flow-tested the canister with the installed new shut off valve (connected 12v power leads to the metal contacts to open shut off valve during air flow test) and......voila....as the song title goes that that smoke blew "Over, Under, Sideways, Down".....by the Yardbirds 1966....lol

Rob

 

Stumped....and you never smell any raw fuel vapors I assume. Would be pretty obvious. Maybe a bad me-sfi?

 

brauhaus313......

Here's my write-up post in October 2022 on my gas fuel smell leak which was a "temporary" repair that didn't hold up. This was a potential quick-fix I gleaned from the C55 Forum. This resulted in me buying and installing a OEM fuel sending unit which cured the interior fuel smell. No issues since the repair.

https://mbworld.org/forums/c32-amg-c...ml#post8647837

Rob

 

brauhaus313......

Now tracing evap canister shut off connector wire as it enters thru a small porthole from the rear fender well into the trunk. Just looking for an intermittent fraying of that wire that may lose continuity when car is moving. So far, no such luck.

Unfortunately, in the trunk's right rear bottom corner at the fender well (removed all trunk liners), I found a solo loose wire with a very small connector at the wire's terminus. The line is "hot" with continuity and I'm at a loss as to its home since I didn't see any empty wire terminals. Here's two photos and maybe, just maybe, you might know what it's for.




Thanks for your imput yesterday as it was much appreciated!

Rob

 

@Robjr

What a happy coincidence. I do know what that plug is. If you had a Sirius tuner in the rear that little plug would slide into the side of a larger plug that has MOST fiber optic lines going in/out of it. The Harman amp in your pic has the same kind of MOST/power/and what I assume are canbus lines combo connector to it. I just happen to have all the rear paneling in my car out right now installing some stereo gear and knew what that plug is right when I saw your pic.

 

brauhaus313....

For sure which is a relief as I thought "why would MB leave a loose "hot" wire in the trunk"? About a year ago now, my PC had a hard drive failure and I installed a new hard drive. Some of my old programs and their corresponding software would not work. Hence, my MB EPC and WIS/ASRA program was lost. Although there's plethora of those "free" programs on the internet, I'm somewhat leery of giving one a try.

In that regard, do you have a wiring diagram/schematic for the trunk electrics?

Again, thanks for your help...

Rob

 

Sorry, I don't have a diagram/schematic, but if you're looking for one to see which way the shutoff valve wiring goes, I can tell you it runs along the passenger side of the car up to the front of the car. It is the wire bundle wrapped in yellow cloth electrical tape coming out of the rear passenger side wheel hump in the trunk. Behind the rear passenger side seat bolster, you will see the yellow taped bundle continue up the car and it should have a tag on it with part #A2035408805.

 

brauhaus313.....

I traced the evap wire up into the gray metal bulkhead then down the rr seat bolster down to the interior footwell sidewall up to the right passenger foot well and up into the engine bay and stopped. I didn't find any frayed wires which is good, Frankly, I didn't expect too, either. As I said in an earlier, I tested for contintuity from the front SAM back to the canister shut off valve (Y58/4).

In light of that time-consuming frolic, I'm buttoning up the trunk and will re-scan to see if P0446 rears its ugly mug, again. If it does, I'll visit my MB dealer AMG tech friend at his house to see if there's another solution.

By the way, what EPC WIS/ASRA program do you use and, also, what odbII scanner do you have? My MB tech friend has a $4000 AUTEL unit and he suggested the Autel 808 which is about $500. I think some research is needed before I pull the trigger.

Thanks, again..

Rob

 

I don't have a program and use a Vident I-link400 for Mercedes. It's just okay. It was relatively cheap and it reads all the modules, but I bought it because it was advertised with the ability to activate the ABS during brake bleeds. Sadly, that function hasn't worked on any of my Mercedes. Maybe there's a process I'm missing. I doubt it does anything more than your Innova. What are you looking for in the 808 above what your Innova does?

 

brauhaus313...

Evap and ABS stuff.......My Innova, according to the quick guide supplied with the unit, was supposed to do that for MB's but it doesn't.

Rob

 

brauhaus313....

Quick update........Visited my local MB dealer and, since both shop foremen are friends, hooked my C55 up to Xentry to check wiring schematic. The tech, for good measure, traced the wiring from front SAM to the evap shut off valve (Y58/4), just prior to newly installed pigtail adaptor. Good continuity to this point which was the same results as my test. However, a closure visual inspection of that pigtail revealed the positive wire was connected to the ground wire female sleeve inside the plastic two-prong connector and the ground wire was connected to the female sleeve of the positive wire!!!

What the f#*@^! WHODATHUNK ...?

Clearly a whopper of a manufacturing defect!!!! Parts supplied a new pigtail and VOILA!!! That nasty P0446 DTC simply evaporated (no pun intended ~ lol) along with CEL.

Needless to say, my shop foremen friends took good care of me and I'm very grateful.......A nice extended lunch for the boys will be on me in the next several weeks...

I'm pleasantly pleased that's for sure......

Rob

 

Wow, that's great news Rob.

Good thing you don't have to replace any expensive parts but ... "What the f#*@^!" indeed.