Evap System

[TrAvELAr]

I've been periodically getting a check engine light (once every few weeks) on my 03 TJ which is calling error code P0456. This indicates a very small leak in the evap system. The most common google response to this seems to be to check the gas cap seal. While I haven't replaced it, it seems to be excellent condition.

My knowledge of where to look next is very limited. One person posted that he changed a hose and clamp and it fixed his problem. I'm not exactly sure what hose or where to look next. Any advice would be appreciated.

[RangerRick]

Have that fuel cap tested to make sure the check valve isn't bad. The seal may look good around the cap but the cap could still be bad. This is of corse assuming the rest of the evap lines are tight and have no leaks in them. Borrow a friends cap to see if the light stops coming on. I found on two of my TJ's that after market locking caps do not work and set this code for some reason so I had to get a factory locking cap from ebay or a dealer. There must be a difference in operating pressure of some caps check valve itself. There are emissions lines you may want to check that run to the frame from the top of the gas tank and to the evap canister under the hood. Also, you may want to check to see if the filler neck hose clamps from the filler to the tank are all tight. You can access them through the plastic flap behind the rear drivers wheel well under the filler on the driver side of your TJ. This is a common code on 97+ TJ Wranglers.


Rick

[TrAvELAr]

Thanks Rick. I'll check things out this weekend when it stops raining (aside from the cap). That I can check out before the weekend.

[TrAvELAr]

Thought I'd post a follow-up to this. After replacing the gas cap, I've got about 1000 miles down with no signs of the check engine light. So far, so good.

[Materdaddy]

Thought I'd post a follow-up to this. After replacing the gas cap, I've got about 1000 miles down with no signs of the check engine light. So far, so good.

As I was reading the thread, I was going to say that I think the code takes a little while to go away after replacing the cap unless you use an OBDII scanner to clear the codes.

[TrAvELAr]

As I was reading the thread, I was going to say that I think the code takes a little while to go away after replacing the cap unless you use an OBDII scanner to clear the codes.

Actually, I just unhooked the computer for 10 seconds.

[Materdaddy]

Actually, I just unhooked the computer for 10 seconds.

That works too, but it might also reset the PCM's "Adaptive Memory" data.