Recently purchased 2004 W211 wagon from a dealer in NY State. Trying to get it through emissions to register it in CT, but every time the Evap Systems Monitor goes into the Ready state the CEL comes on. Code is P0446, with a subcode of P2025 and text of Y58/4 Activated Charcoal canister shut off valve. When I first got the car we were getting a P0455 large leak, which the dealer diagnosed as being the rear shutoff (purge?) valve. They replaced the valve, but ever since we have been getting these p0446/P2025 codes. The dealer has now given up. Does anyone have any brilliant suggestions? Unfortunately I do not have a bi-directional ODB tool, so I need an experienced mind to point me at the problem if possible.

That’s still the vent valve system throwing the code. The reason it waits to set the CEL until it goes to ready is that it doesn’t check the system until the ready signal is received. P0446/P2025 is also triggered when there is an error detected in the evaporative emission temperature(???) circuit.

It could be bad sensors or wiring faults. Since it was at the dealer, I would assume they looked for brittle or cracked lines and a cracked canister. The canister can crack at the mounting points and is hard to see.

I have seen some say replacing the gas tank cap can fix this error. That would be a relatively inexpensive guess, but no guarantees on it working because that’s usually P0457.

Thank you for these comments, as they triggered a thought. We weren’t getting this specific error until after the purge valve was changed (EVap system would go ready without a CEL coming on), which my little brain computes as meaning the error was introduced by the change. I’ve heard it said that an aftermarket valve replacement often has the power and ground wires reversed in the pigtail attachment. Anyone have experience of this perhaps?