1997 Chevy s10 4x4 zr2 4x4 with the 4.3L (x vin #) vortec engine. 286K miles, 100K on the engine. I've gotten this code once before about a month ago, but went away when I changed the gas cap. It just came back tonight when I went to start it after gassing up. Could it just be the gas cap again? I really don't feel like messing with the canister or anything. Ugh, too much electronic garbage on cars nowadays!

 

could be the cap not on right but I would do a smoke test that will pinpoint the leak if there is one, my daughters equinox had that code , did the smoke test found smoke seeping from wall of canister I just put a layer of marine goop on it, it has been fine now for just over a year

 

1997 had a "W" engine. The "X" engine was not used in S/T series vehicles until 2003.

Following the steps in this link will locate the problem. https://blazerforum.com/forum/diagno...plained-35145/ P0440 covers a ton of stuff, the first couple of paragraphs explain what can set it.