AdmirN

I need some input for what could be causing my check engine light to go off every 1-2years.

Heres the short story.
Bought my 08 scion tc in 2007, took it the dealership for a check engine light on jan 2009. Codes pulled were p0441, p0455, and p0456. Which has something to do with the EVAP. They did a evap test and it passed with no problems so they just replaced my gas cap and light went away.

Well every 12-24 months my check engine light goes off, and I get the same EVAP codes. I had to replace my gas cap 3/4 times now already. I just replaced my gas cap yesterday, drove 50+ miles and it went away. The time before this one was on Feb 2014, I replaced the gas cap, drove around and light went away. It also seems like this always happens during the cold seasons.

I was going to take to Toyota to get a diagnostics but the light went away so it would be kinda pointless now. Does anyone know what the issue could be? I shouldn't be having to replace the gas cap so many damn times. And yes I replace it with the original Toyota gas cap. My moms Camry with over 120k+ miles never had this issue.

TTCCC

When the light comes on have you tried unscrewing the gas cap then putting it back on and seeing if it goes away? You shouldn't be replacing them that often. I have only had to replace one on my 2008 since buying it new.

Basebllstar

Why wouldn't you try clearing it to see if it's a fluke?

AdmirN

Sorry I guess I should of mentioned that. I did try cleaning the cap and around the tank and see if that would of helped. Unfortunately it didn't.

bbsciontc

I get it from time to time. Usually it's because the attendant didin't tighten the cap all the way. I just re-tighten it and it goes away on its own.

I did have a leak in one of the hoses going to the VSV (vacuum switching valve) under the hood. It was a small leak due to the hose fatiguing where it was clamped to a hard line. I just undid the clamp, pushed it on further so the hole was no longer letting air leak and it was fine ever since. That was about 5 years ago.

AdmirN

I always pump my own gas and I make sure I hear it click 2/3 times so I know it's on tight. Could you send a pic of the hose you are talking about. It's just weird when I replace the gas cap it goes away then.

62Fender

Filling the gas tank too full can inundate the breather pipe that runs adjacent to the fuel filler pipe. The owners manual advises to stop filling when the fuel pump automatically cuts off, (typically ~1.5 gallons shy of "slam full".)

Check your fuel cap leash when tightening the cap. My cap leash caused the cap to roll ~1/8" counter-clockwise after tightening so I took it off. It comes off w/o breaking so you can always put it back on if needed.

AdmirN

Thank you, I will avoid overfilling it and see how that goes. I only do it 50% of the time.

I've noticed that leash as well, and was a little concerned about that myself. Since the cap takes very little effort to unscrew it, I will remove it from the cap.

62Fender

You're welcome. Toyota also says over fueling risks gooching the evap canister.

Your situation sounds like mine. I overfilled because I hate gassing up. I got the gross leak codes so I bought a new cap. Still threw the CEL so I stopped overfilling. The combination of new cap/ not overfilling fixed the problem.

AdmirN

The cap seems so sensative. I told scion crop my situation and they investigated but they are taking the dealers word whatever they say. But the dealer is just BS and wasn't willing to help and do a free duagnostics when I took this car in for the same situation back in 2009. But the lights off now so well see what happens next.