These codes are EVAP system codes related to the vent solenoid. The P0449 is for the valve, the
P0440 is a general evaporative emissions system failure, caused by the P0449.
This part is in the back of the car, usually in the drivers side wheel. It does just what the part is
called, it vent fuel vapors in the emissions system.
A way to test it is to apply voltage to one wire, and ground to the other on the connector. If it is
functioning, it will click. It won't if it is not working. Another way is to give it a few taps. Most of the
time they just get stuck because of dirt and moisture getting into it. The best way to tap on it is
with a scanner that that you can use to command the vent solenoid on and off. But if you do not
have one, you may get lucky.
If the test above do nothing to help, then the solenoid inside is shorted out and it will have to be
replaced. There is just a small bracket that hold it on. One repaired, the codes will have to be
cleared from the computer to get the check engine light to go off.
See picture below of how vent valve look.
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1999 Buick Century P0440 and P0449