Check engine light

Chevy / GMC - P0446 EVAP System Vent Performance Problem - YouTube

Its what is called the EVAP. system the code is for the vent solenoid .Gas vapor in a vacuum is drawn from the fuel tank when this vent is commanded to be open drawn into a canister filled charcoal and stored until the canister purge solenoid is commanded to open .
This happens when the engine speed is at a higher RPM level and is supposed to send the vapor to the engine to be burned instead of VOC'S going into the atmosphere .But its a crazy lie the last time I filled up more VOCS got into the atmosphere then a gas tank vent could do in 6 month or so .
You can try cleaning the filter in the vent solenoid it might work but the part is about 70 dollars its in the rear between the tank and the canister look for hoses .

need more info if high mileage on original fuel pump check pressure because if pump is not pumping enough fuel it will not open fuel pressure regulator and will give you same issue

Trouble Code: P0446

EVAP Vent Control Solenoid Circuit Malfunction

Possible Causes:


Vent solenoid circuit open, shorted to ground or to power (B+).Vent control solenoid is damaged or has failed..PCM has failed.TSB 00-060 (7/00) contains information related to this code.Trouble Code: P0455

EVAP System Gross Leak (0.080") Detected

Possible Causes:


.EVAP control system pressure sensor is damaged or has failed.EVAP purge solenoid or canister vacuum line loose or off.EVAP purge solenoid is damaged or has failed.EVAP emission canister is dirty, restricted or full of water.EVAP canister vent control valve is damaged or has failed.Fuel tank cap loose, missing or it is the wrong part number.Fuel tank temperature sensor is damaged or has failed.Fuel tank vacuum relief valve is damaged or has failed.Large leak in the EVAP canister or in the fuel tank area.ORVR system is damaged or has a large leak in a component.Refueling control valve is damaged or has failed.Vacuum hose leaking between intake manifold and Purge valve.Here are the codes,take part back and get refund.

http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?pageId=0996b43f80380329#hd1-1-28 Here is what is listed for problems,couldn't find codePO446,click on link to view.

po305 is related to missfire on #5 cylinder
po440 is related to fuel tank pressure
pO441 is for evaporator purge flow malfunction
po446 relates to vent control valve electrical circuit malfunction

missfire is seperate from the other codes
as for the other three codes replace the vent control valve solenoid located near the charcoal canister the oth3er codes can relate to a faulty solenoid

after replacing light will only go out if you clear through a scan tool or three drive cycles of over 10 min each

P0446 Evaporative Emission System Vent Control Circuit.
The following are descriptions of all Evaporative possible codes:

P0441 Evaporative Emission System Incorrect Purge Flow
P0442 Evaporative Emission System Leak Detected (small leak)
P0443 Evaporative Emission System Purge Control Valve Circuit
P0444 Evaporative Emission System Purge Control Valve Circuit Open
P0445 Evaporative Emission System Purge Control Valve Circuit Shorted
P0446 Evaporative Emission System Vent Control Circuit
P0447 Evaporative Emission System Vent Control Circuit Open
P0448 Evaporative Emission System Vent Control Circuit Shorted
P0449 Evaporative Emission System Vent Valve/Solenoid Circuit
P0450 Evaporative Emission System Pressure Sensor/Switch
P0451 Evaporative Emission System Pressure Sensor/Switch Range/Performance
P0452 Evaporative Emission System Pressure Sensor/Switch Low
P0453 Evaporative Emission System Pressure Sensor/Switch High
P0454 Evaporative Emission System Pressure Sensor/Switch Intermittent
P0455 Evaporative Emission System Leak Detected (large leak)
P0456 Evaporative Emission System Leak Detected (very small leak)
P0457 Evaporative Emission System Leak Detected (fuel cap loose/off)
P0458 Evaporative Emission System Purge Control Valve Circuit Low
P0459 Evaporative Emission System Purge Control Valve Circuit High
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At least the cap isn't loose for the gas tank.

I would clear the code with an OBD-II Scanner 'erase code' button, and see how long it takes for it to come back.

you have to understand that there is a leak in the system other than the gas cap for the evaporative system. The system needs to be professionally closed, and smoke introduced into to find the leak, and a through component check, eg.. purge valve vapor canister vent solenoid all functioning correctly

P0446 This indicates that a part of the EVAP control system is no longer fuctioning correctly. EVAP emission canister purge is contolled by a valve which allows engine vacuum to pull stored fuel vapors from fuel tank into the engine to be burned, rather than be vented to atmosphere. 
A vacuum switch is used to detect when flow exists. If the PCM commands purge and sees that the switch is closed (indicating no detected purge flow) P0446 is set.

When the vapor pressure rises to a specified point, the ECM opens the VSV for canister closed valve. Pressure will increase rapidly because of the air allowed into the system. No increase or an increase below specified rate of pressure increase indicates a restriction on the air inlet side. The ECM closes the VSV for pressure switching valve. 
This action blocks air entering the fuel tank side of system. The pressure rise on the fuel tank side is no longer as great. If there was no change in pressure, the ECM will conclude the VSV for pressure switching valve did not close.

It is probly your evap canister vent valve is restricted. GM has a new design assy that repositions the vent so dirt wont plug it up, i suggest taking to a dealer to make sure, thay can use a tech2 to acurately diagnose the concern.

Good news is Likely, no symptoms will be discernible to the driver, other than the illuminated Check Engine Light.
Bed news A code P0446 could mean one or more of the following has happened:
Bad vacuum switch
Broken or damaged EVAP line or canister
Open in PCM purge command circuit
Open or short in Voltage feed circuit to Purge Solenoid
Faulty purge solenoid
Restriction in EVAP solenoid, line or canister
Corrosion or resistance in purge connector
Bad PCM

Good luck and hope this helps

p0446 is an evap code for incorrect purge flow, check the rear vacume switching valve. its above the rear sub frame