I'm getting a check engine light ONLY after filling the gas tank. When I read the code, I get:
P0455 (M) Evap Leak Monitor Large Leak Detected A large leak has been detected in the evaporative system.

The thing is, it ONLY comes on after filling the gas tank. I have a el-cheapo code reader and can reset it myself, so when it comes on I reset it. Until the tank is below 3/4, it will come back on. Once I've used 1/4 of a tank, it will not come back on until I get gas again.

I have replaced the gas cap with a brand new one from Autozone, but can't seem to figure out what else may be causing this. Any suggestions?

 

try replacing the gas cap... could be bad, i know this has been a problem on Chevys

 

Re-read the last sentence in my post. I already replaced it and this is still happening.

 

X2 buy the cap from a real parts store. I had six bad injectors in a row from those guys. #### autozone. I won't set foot in there unless I have to.

 

x3 on the gas cap they're only a couple bucks or maybe you have a buddy with an xj that will let you try his. I would also check all the hoses to the gas tank I think there are 2 vacuum type hoses going to it. I think one is for vapors in the tank and one is a fuel return but don't quote me on that.

 

There is a number of things it could be. I'm tracking down the issue myself. I threw both a P0455 AND P0456 (large and small leak code respectively). Keep checking around the site and you'll find lots. I'm doing that now myself.

 

I forgot about this thread, lol.

The solution was simpler than buying or checking anything...
I just had to stop topping off the gas tank. Apparently I was over filling it and causing fuel to get into the evap system. *shrug*
Either way, my fix was to not top it off. When it clicks, shut it off.

I haven't had a light since.

 

He did didn't you read the post? wow

 

Agree. Don't try to get the last 87 cents worth of gas in your tank. Bad habit and you gain literally ZERO benefits except an extra 4 miles before your next fill.

Doing that can create excess hydrocarbons which get picked up by the emissions system as it thinks you have a fuel leak.

When it clicks, SHUT IT OFF.

 

I know for myself it won't be any small issues like topping of the tank (which I just carry an extra 2gal can for that)or gas cap. I can't wait for warm weather.