CEL confusion...

Every 200 miles or so the CEL light comes on. Each time I pull the code and it's the EVAP system code. Then, I clear the code, go unscrew and retighten the gas cap, start up and drive away. The light stays off for another couple hundred miles. Is it just a bad gas cap, a quirky ECU, or something more serious? I averaged 18.5 MPG last tank and the vehicle runs smoothly, no funny noises or anything. Any ideas?

I would consider replacing the gas cap first - it's the least expensive option.

Reason for the long delay before the MIL turns back on is the fault has to show for a few drive cycles 1st before it will turn on the MIL.The EVAP system does not constantly test itself either,maybe everyother drive cycle if your lucky.

Which code does it throw?
I had a very similar issue with my VW GTI. A friend here at work has a recurring EVAP code too. With me I would drive until it went away on its own. Sometimes the gas cap light would come on. Sometimes not.
My cure was to finally get a new cap and it went for good. Though sometimes I would stop on the side of the road to clear the code. That light really began to tick me off.

I guess my question is, if my economy and performance is still good, can I rule out that this is a serious issue? I'm not very familiar with EVAP systems, but when I had the code pulled (P0441, or P0411 I think?) it called it a vacuum leak. If there was an actual leak in the vacuum lines somewhere it'd run roughly, right? My plan is to swap the gas cap for starters. If that doesn't take care of it, what should I look for/look into next?

jschenck said:

I guess my question is, if my economy and performance is still good, can I rule out that this is a serious issue? I'm not very familiar with EVAP systems, but when I had the code pulled (P0441, or P0411 I think?) it called it a vacuum leak. If there was an actual leak in the vacuum lines somewhere it'd run roughly, right? My plan is to swap the gas cap for starters. If that doesn't take care of it, what should I look for/look into next?

Click to expand...

first find out what code(s) you are getting. A gas cap will not fix either of those codes.

P0441 Evap Purge Flow Monitor Insufficient or excessive vapor flow detected during evaporative emission system operation.

P0442 Evap Leak Monitor Medium Leak Detected A small leak has been detected in the evaporative system.

P0443 Evap Purge Solenoid Circuit An open or shorted condition detected in the EVAP purge solenoid control circuit.

P0455 Evap Leak Monitor Large Leak Detected A large leak has been detected in the evaporative system.

P0456 Evap Leak Monitor Small Leak Detected Leak has been detected in the evaporative system.

look at those. I'd say only the P0456 would be the gas cap IF it isn't any of the hoses coming off of the carbon box back in front of the gas tank. I had just a couple weeks ago the P0456 and when I went to get gas the cap was loose. (i think my 6 year old got curious) but anyway after driving 72 miles the CEL went out.

you may be looking at a purge solenoid. check out this thread:
http://www.jeepkj.com/forum/showthread.php?t=35504&highlight=codes

The code is PO441. What is the common cause(s) for this code? Any help would be great!

just got the p0456 code today. gas cap felt tight so i might try looking for that tube by the tank to see if its bad.

I got code 0441 once on low mile KJ and it turned out to be the non factory locking gas cap/seal was bad, even though cap was new.
Went to dealer picked up a locking gas cap from them and have not had the code return.
Aftermarket gas caps can literally suck.

What are the steps to test the cap? (besides setting a P0456 )

I've been getting P0441 for the last year+ on and off, on and off... I've replaced the gas cap with one from walmart and then with one from the Jeep dealership about 9 months ago. The two looked identical to me and I checked them pretty thoroughly too. But they were not locking gas caps, but the normal screw on and click type. Either way the codes continue. 18.5 mpg for me.