CEL - P0442 EVAP Small Leak

I have a 2000 GMC Jimmy 2dr, 4wd, 4.3l v6, with 104k miles.

Alright, that pesky little CEL has been coming on lately. Code is P0442 EVAP Small Leak. The gas cap has been replaced with an aftermarket cap purchased at carquest (and definitely tightened) but that doesn't seem to have solved the problem. I had the code reset and then replaced the cap. I drove it around all weekend (interstate, city, country roads) multiple times). And then this morning, it comes right back on (oddly enough, that happens to be only when my wife drives it).

I've looked through a few manuals but they don't seem to give any good indication of where everything is that I should be checking. I don't know where to start looking for hoses that might be bad or whatever else might be bad.

We don't have emissions inspections in my state, so I'm not concerned about passing anything like that, but just curious about where to start and what direction I should head in. I've searched the site on this topic, but haven't found a thread that might help.

Any ideas would be appreciated.

I would try a GM dealer cap.
Do not fill tank with engine running.
Is the filler neck where cap goes on dented up?

The code is what it says a small leak.

First step on repair is to see if fuel tank will hold vacuum without leaking down.

Many places they an leak.
Hoses and vacuum lines and vent valve and canister.
If a good gm cap does not fix it start looking for a small vacuum leak.

A good engine scanner will run some test and help find some leaks.

For the real hard to find leaks most dealers and some repair shops have a smoke machine to test them.
Good Luck

My 99 Sonoma had a P0442 code that turned into a P0440 code (malfunction) - I could smell gas when I opened the fuel door. Turns out the filler neck was rusted and causing the problem - I sanded the neck and coated it with an epoxy - the light has not come back since (at least a month).

Mark, that's interesting, especially since this is exactly what I'm smelling at the fuel door. Did you occasionally smell it in the cabin at all?

MT, quick question on the gas cap. If an aftermarket cap is made according to OEM specs, why are these necessarily worse than what came with the vehicle? I've seen it all over that you should buy one from the dealer, but why sell these aftermarket at all if they're not good?

In general if anyone knows, who made these caps for GM? Is it AC Delco? I purchased my aftermarket cap from CarQuest; the part is made in the U.S. but I can't remember the company that made it for CQ.

I went the same way - I originally purchased a new gas cap from CarQuest - I then bought a new one at the Dealer - no difference - and yes I occasionally smelled gas in the vehicle - mostly when I stopped.
I actually took off the gas cap and coated the outside of the filler neck (from the top to where it contacts the body) with Dow Corning Vacuum Grease and then replaced the cap. The light stayed off for a week - I then took the time and cleaned the filler neck and used the epoxy. Hope this helps. BTW - a new filler neck is about $100.00

I appreciate the responses. I'll take a look at all suggestions, see what happens, and post back.

Mark, what epoxy did you use?

I used a gas tank repair epoxy - got it at Autozone - but later found it cheaper at Advanced Auto. The stuff is a stick that you blend together - use small amounts as its working time is kind of short.