OBD2 "GOTCHA!!" (Page 1/1)
Raydar OCT 06, 11:37 AM
I've never seen this before, so I'm going to share it here.
My wife filled up her Odyssey van, last week (at Raceway.) Shortly after she filled up, the "check fuel cap" light (seriously) came on. (She was busy and decided to do that when she got home.) The next time she started it, the "fuel cap" light was out, and the "check engine" light was on.
She checked the fuel cap and seal, and found nothing.

When she got it home, I checked the fuel cap and found nothing.
I connected my scanner. I forget what the two codes were, but the messages were "evap system minor leak" and "evap system gross leak".
The van ran fine. No noises. (I was expecting a hiss or whistle, or something, from the canister or the evap system hoses. Nothing.)

Anyway, she had to go out of town this weekend. I didn't have a chance to have it tested before she left, but I didn't see a reason to worry about it, since it was running fine, had no gas smell, and had no other codes.

She filled it up again yesterday. As soon as the "fresh" gas got into the system, the light went out. (Remember... We both had removed and checked the cap, so I don't think that was the problem.)

So... WTF?! I can only conclude that there was something in the Raceway gas that the van really didn't like. (This was the speculation when we found nothing wrong, at first. She said that it ran a bit strangely, shortly after the fill-up, but that the problem went away.)
I've never heard of this before.

Edit - I guess the "Cliff's Notes" version of this should be, "If your check engine light comes on, it could be caused by bad gas."

[This message has been edited by Raydar (edited 10-06-2012).]

skuzzbomer OCT 06, 04:00 PM
Newer Chryslers have an issue, where a loose fuel cap will trigger the same codes you mentioned. Tighten the cap all the way and it'll cycle the light off after a couple drives.

Haven't run into anything like that on any of my cars, though.
Raydar OCT 06, 06:15 PM

quote
Originally posted by skuzzbomer:

Newer Chryslers have an issue, where a loose fuel cap will trigger the same codes you mentioned...



It's not just newer Chryslers. Anything with OBD2 will trigger the codes with a loose cap. I've probably had it happen, at one time or another, on most of the OBD2 cars that I've owned.

The problem is, the cap was not loose. It was removed and checked at least twice. There was no leak.
The car was driven most every day for a week. The codes went away when fresh gas was added to the tank.
E.Furgal OCT 06, 07:30 PM

quote
Originally posted by Raydar:


It's not just newer Chryslers. Anything with OBD2 will trigger the codes with a loose cap. I've probably had it happen, at one time or another, on most of the OBD2 cars that I've owned.

The problem is, the cap was not loose. It was removed and checked at least twice. There was no leak.
The car was driven most every day for a week. The codes went away when fresh gas was added to the tank.




the vent plunger in the center of the cap is failing.. the seal most likely is fine, thats not what fails.. flip the cap over and look at the center.. that plunger is leaking..
Raydar OCT 07, 12:36 PM
Thanks for that. I'll have a look.

Much appreciated.
E.Furgal OCT 07, 02:57 PM
think about it. if it was the orind seal.. we'd stock and sell a ton of them , instead of selling the whole cap
Raydar OCT 07, 08:29 PM
Between the two of us, we had the cap off and on several times.
Odd that the situation cleared up as soon as different gas got into the system.

But your idea makes sense. She just got home a bit ago. Can't check it now. It's too dark.
jaskispyder OCT 08, 11:50 AM
My Aztek does this all the time. Somewhere there is a problem, and it isn't the gas cap. It is in the EVAP venting system and I am not going to fix it.
tesmith66 OCT 09, 12:49 PM
My Silverado did this off and on for a year after I bought it (brand new). I finally bought a cap at Auto Zone and it went the remaining 265000+ miles with no issues. The factory caps are usually the culprit.
Tigger OCT 10, 03:10 PM
Find out what code it threw, p0440, P0442, P0446?


quote
Originally posted by jaskispyder:

My Aztek does this all the time. Somewhere there is a problem, and it isn't the gas cap. It is in the EVAP venting system and I am not going to fix it.



Not being the cap likely it's the (evaporative) vapor canister purge valve or vent valve. The canister purge valve on that GM is probably located behind the wheelhouse and quarter panel up by the filler neck. $16-$20 part and can be replaced in less than an hour.