Have you first tried replacing your fuel cap and clean the fuel filler neck? Small leaks to EVAP system can be very challenging to find, which may also include problems with the vapor canister and associated valves (which are located near the fuel tank driver side)
I'd check the cap first as Jay suggests. If that's okay and there are no cracks in the cap seal check the purge valve. I've had to replace mine twice. Fortunately they sell a lifetime warranted one at Autozone and they're easy to pop off and install. Cracked vacuum lines will also cause that code so check around a little first.
Like I stated in another post, check the vacuum line to the brake booster, if it's like my Lesabre there will be a vacuum test fitting just as the hose leaves the intake manifold in the back top of engine. It has a rubber cap on it that rots off from the heat. This will give you this code as it springs a vacuum leak and then when the cap rots off completely, it will graduate to P0449 or something like that, stating that the on-board computer can no longer compensate for the size of the leak. I also had a smell and a little smoke from under the hood as the rubber cap had fallen across the exhaust manifold near the EGR valve and was burning/melting.
