How do you fix error code p0446 on a 2001 Saturn SL1 you tightened the gas cap and cleared the code but it keeps coming back?

P0446 Evaporative Emission Control System Vent Control Circuit Malfunction. it could be that the evap system purge solenoid is not working properly.

Most likely cause(s):

If you operate the car in a high dust environment, you may have a vent valve and its filter that is plugged or you may have a plugged charcoal cannister (some GMC vent valve filters do not filter dust and dust fills the cannister). If you overfill the gas tank, look for a plugged cannister.

Other causes:

You may have a bad gas tank vacuum sensor or vacuum sensor circuit. Your engine vacuum valve may not open or close all the way, the coil might be open or shorted or its control circuit inoperative. As suggested above, your evap purge (vent) valve may leak when shut, have a shorted or open coil or the electrical control circuit to it might be inoperative. Likely things to check:

The vent valve is always open with electrical power off, so pull the hose off and with a hose and blowing with your breath, insure that gas will easily pass through the valve. If it is restricted, clean or replace the valve.

Pull all three hoses off the charcoal cannister and confirm that air will easily pass from the large vent side to the two smaller tubes and vice versa using a small rubber hose and pressure from your breath. Do not suck on the line. If it is restricted, clean by turning upside down and with low pressure air (block one of the small tubes), blow toward the vent valve side while sharply tapping the cannister and looking for dust coming out. If it is still restricted, replace the cannister. If the vent valve and cannister check out OK, you will have to trouble shoot each remaining component with a scan tool, vacuum gauge and other specialized test equipment.