[waybomb]

With the fuel tank vent valve disconnected from the 2003 ML 350, should it be normally open, meaning, you can blow through it with no restriction noticeable?

 

[Witek_M]

What are you calling vent valve? One under the hood or one by spare wheel?

 

[waybomb]

The one in back, with the attached hose that goes behind the bumper cover.

 

[Witek_M]

That is called charcoal canister shut off valve. Closed only during vapor leak test. Normally open so vapor can exit tank through charcoal canister.

 

[waybomb]

Can you tell me how to check for operation during the energized cycle, and when does it happen?
Can I pull the plug and check for voltage, and what voltage am I looking for?

 

[Witek_M]

It gets 12V (blue wire) from fuse F1f22, ground (pink wire) from engine control module. What kind of problem are you having?

 

[waybomb]

I have a cel forgot what code but for a leak in the vapor system.
I changed the engine bay purge valve cleared the code and it came back.
So I bought a cheap smoke machine on ebay and plugged it into the line leading away to the back on the engine purge valve.
Smoke came out of the rear vent valve.
So now I have to troubleshoot it, before I pay what looks to be about three hundred bucks.

 

[Witek_M]

Apply 12V to shut off valve and run smoke test again.