This is stupid. Maybe it'll help someone else down the line.
My car was due for NJ OBD-II emissions inspection. It failed. I was getting a CEL for P0441, "Evaporative Emissions Systems -- Incorrect Flow Detected."
A mechanic friend said one of the factory solenoids was dead. Replaced it for $60. No change. :(
Then we found a BIG crack in the custom downpipe. That was probably from a winter pothole combined with the fact that I need new motor mounts. Obviously, that impacts emissions flow.
So I bought a new downpipe.
Still had the CEL!!!
(Side note: couldn't complain because the DP needed replacing anyhow. For the record: this was NOT any fault of TurboTim re: how he built the exhaust system. I still recommend his work a million percent.)
A related problem was that the other emissions tests during the factory ECU readiness cycle, such as the O2 sensors and the cat converter test, weren't even being tested because it kept getting stuck on the evap system test and not advancing. Kept getting the "not ready" message on my code reader even after hundreds of miles code-free after clearing it.
Finally, on a whim and feeling very skeptical, I cleaned the bottom of the gas cap and the top of the filler neck.
You see where this story is going, right?
Code was gone (even though the reader STILL said the evap system was "not ready" for testing) but now the other emissions stuff was all-systems-go.
So, if you get P0441, then before you do ANY other work, try cleaning the gas cap and filler neck. It might save you a ton of hassle!
In which case you owe me a