2008 Impala, 3.5 V6. The CEL was on this morning, and the OBDII reader determined that it was from a P0455 code, meaning the Evap system has a leak. I bought gas over the weekend, so it's possible that I didn't tighten the cap properly. After doing so, the light remains on. Are there any common problem areas with this model that I should check? I don't smell any gas fumes. Also, would this be considered an emissions problem that the dealer has to correct for free? The car is now 9 years old (maybe 10, depending on when in the model year it was produced), but has only 56K miles.