2005 Sierra P0446 code
 

I have a P0446 code I can't get rid of. This is what I did so far. Changed canister vent valve, and also upgraded to remote intake filter to engine compartment. Changed purge valve on engine. No problem with filling gas tank, or no smell of fuel at all. The code says "Emissions Vent Control Malfunction". Anyone have any ideas. Thanks Bruce

Well ... I was gonna say if you have a high end scan tool that can control functions on the car, I can tell you how to test it. But chances are, your vent valve has an open/short in the wiring if you've already replaced the valve.

Honestly, usually all I do for vent valves is use the tech2 to command the valve closed, then smoke the system. If the valve is commanded closed, and smoke still comes out, then replace the valve. If the valve stays open no matter if it's commanded open or closed, put a test light on the terminals and see if the power/ground toggles the light on and off when the vent valve is commanded on/off.

Without a scan tool, I really don't know what to say ... that's how I'd do it. Borrow one, take it to a shop, whatever, but that's really the only way I know of how to toggle that valve open/closed to do testing.

p0446
 

I had my truck scanned. The tech said both the vent valve and purge valve were working. I read other posts, and found it could be a fuel tank pressure sensor. I asked the tech if he could test that sensor, but he could not find it on his Snap On scanner. Does that mean I don't have a tank sensor? Thanks Bruce

I have a 09 sierra 5.3 and have changed tank press sensor. and evap purge valve and cleared po446 code several times and the code comes back after a day or two. any suggestions how to clear it for good?

Mine had a bad fuel tank pressure sensor