ML350 - p0446 CEL code...Charcoal Canister shut off valve
 

Hi guys,

This is on a 2005 ML350 that we just purchased.
I am struggling to figure out how to find what part is faulty without just throwing parts at it as I know the system has a couple components.

I cleared the code, and it came back immediately on the 2nd start.

Anybody here dealt with this code before and can point me in the right direction to find exactly what is causing the CEL? I've spent hours on google now and I cannot find any definitive tests to help guide me on where to start.

446 is the vent valve getting stuck open or closed. in any car in USA its at the back of the car near the fuel tank or on the tank. Its a pretty common failure on GM vehicles, you can look at those to get an idea of what you are dealing with.

Then you can dig into your vehicle to identify the bits n pieces and resolve it.

This can also be a tank pressure sensor failure (look at the freeze frame data to see when the fault occured)

A new vent valve is about $260, so is there a way to test if my one is bad?

On most Mercedes the valves are Identical, so steal one from a +2000 W208/W220/W210 from the junk yard. Most cars have this valve inside the left rear inner fender..

This code can be nightmare along with P0455 "gascap code"...

If it comes on right away(second start like you say), but no drive you may have open or shorted line to the canister purge valve-easy fix

If it comes on after a drive cycle, you are in for it-In troubleshooting, You may end up where I'm at smoking the system up, and found a leak of intake vacuum on the plenum of the intake manifold on one of the rubber rings on a M119

I have been on it for months, but their is procedure in DAS to test these EVAP valves..

I will post some links that may help you later...

Martin

PS.. most of these valves just have two wires, and you can power it with 12v, and the valve is normally open, yet when powered if you blow on the nipple coming from the charcoal canister the valve should shut.. Current draw is low under an amp maybe more like 300mA... Some say you can clean the valve. Well, I tried that, and ruined mine...

It does come on immediately with no driving on the 2nd start yes.

I agree the diagnosis has been a pain because the fault code does not mean it's that part.

Since you say you believe it is likely a wiring issue, I'll see if I can check the wiring this weekend with my DVM and see if I can be sure it's getting. 12v

EDIT: Found the problem:

http://w124-zone.com/downloads/photo...arcoalwire.jpg

I cannot find the other end of the wire and its hidden up under the chassis so I cannot tell where it goes. Does anyone know where it enters the chassis or have a wiring diagram?

Found the other end behind the driver rear tire. I can't figure out how this happened...but it is what it is. I'll get some wire since I dont have any (18?)ga and get it soldered and we will see if that fixes the CEL!

http://w124-zone.com/downloads/photo...rcoalwire2.jpg

Also found bad upper ball joint (split)...so adding that to the list!

Hey I'm back, but hd some problems on my end, so do you need the info still?

Martin

Well done that man !...we'll can that a FIX. Will put that in my index.


.

Update: last week passed smog after 2 days and about 50 miles of driving to reset the readiness tests. Got the transmission fluid fully flushed, air filter, battery and front/rear diff fluid. Drives great!

$3 fix for the CEL...can't ask for any better result even though finding the problem was a pain.