[shifty]

Thanks for the discussion guys. Appreciate it.

Originally Posted by 95 S_Trucker

P0446 is a vent malfunction. It’s not a leak code. You would have a P0440 or a P0442 if there was a leak somewhere.

It’s definitely not the fuel cap.

This is what I was wondering. I know P0446 has been caused by cap on both our Toyota Highlander and a friend's Camry. Granted, that's Toyota, different beast.

Is my understanding correct on the EVAP system?

I believe: My model has the EVAP canister and solenoid mounted up front between aux battery tray and AC clutch. That has two lines coming off it - one to the intake for re-burn, one back to the tank, which is expected to be sealed. For the PCM to understand whether vent/purge is necessary there's a 3-wire pressure switch on top of the tank, next to the fuel pump, which the PCM uses to monitor vapor and pressure levels, decide if it's necessary to open up the solenoid on the canister, releasing vapor into the intake for re-burn, or throw a code in case of malfunction (leak, high pressure, etc.)

Is this accurate?

What I don't necessarily understand is what specifically is causing vacuum on the tank - Full pump sucking gas out of the tank? Then the solenoid is releasing pressure? Does the gas cap not at all act as a high-pressure limiter on the tank side of the system?

I swear my '03 Sierra had a vent valve towards the rear, had mine replaced under warranty before selling the truck, was clogged. Is the solenoid on the EVAP can the equivalent in this case?