It's finally time to fix my wife's 1999 Trooper. Since we bought it there has been a strong gas smell after you drive it, even the next morning in the garage. It also has the CEL on and I just scanned it and found code P0440 - Evap/Emissions. I'm assuming the gas smell is the evap system leaking out fuel vapor?

I crawled under the car and looked at the tank and the lines running forward until they disappear above the transfercase. There's no obvious damage or wet spots or extra clean or extra dirty spots that would indicate fuel coming out. There's a rectangular box above the rear axle that I believe is the evap canister and it looks to be intact. I'm not sure what other parts are involved with the evap system or where to find them or how to test them.

Help?

Is this a common occurrence with a simple fix?

Thanks in advance.