Originally Posted by Ricard350

I had the same thing happened to me, u did the right thing first u changed your gas cap. So ur cap is now out of the equation.

Mostly your gas tank vent selenoid is toasted and is open all the time. That selenoid is there to help vent the tank during refueling if i remember.

U have that warning displayed and a check engine because ur truck failed the gas tank pressure test and it gives u a vapor leak check engine code. The truck ask to tightnen the fuel cap just in case if it wasent.

At my local GM dealer when I explained the sympthom and told them i replaced my gas cap he knew that if was probably the selenoid.

He used his OBDII TECH 2 scan, and initiated a special test that cycle the selenoid on and off and test the seal and it failed immidiately.

So the selenoid is directly installed on the frame as u can see
N2 VAPOR CANISTER & RELATED PARTS (LQ4/6.0U);. Fits: Hummer H2 | Nalley Buick GMC Brunswick

item number 5.

So it costed my 45$cnd and if took .2hours of time for a final price of around 85$.

He ran the test after and it was a pass. and no more Tightnen fuel cap warning.

I just dont know why ur dealer could not think of that.....

Srry of my bad french canadian learned on the fly written english.

keep us informed

David

Originally Posted by phunkyhalloween

I had the same issue with my 2003 H2. I replaced 3 items on my truck, the gas tank canister that is under the truck attached to the frame. Also I replaced a sensor on the top of the motor can't remember what it was called, it was on the top of the manifold on the front, under the plastic cover. Last I replaced the sensor on the gas tank, located on the top of the tank. It was the most expensive part but replacing them three parts fixed the problem. Just to let you know, disconnecting the battery does not clear the computer, the code will stay in the computer for up to 500 miles or so. The total cost of parts was less than 200.00 and you can replace the parts yourself because labor will cost at least twice that. You can only get the parts from the dealer, most parts store don't carry those items.

Originally Posted by Ricard350

Glad to know that it fixed the issue, now your H2 computer dosent think u havent tightned enough ur gascap.

As for ur engine code, disconnect your battery for 5-10 min then reconnect, it will clear all codes, and ur radio clock too.

Its a small price to pay to get rid for that annoying CEL.

cheers!

Originally Posted by madmajd

Hello everyone
I am the proud owner of a 2007 Hummer H2, bought it about 2 years ago, and put about 9,000 KM on it over those two years (now at 97,000). A while back (can't remember exactly when) my car told me "tighten fuel cap", so I tightened it, and drove, and it told me that again while driving, then came the check engine light. Its been like that for a long time now, it would tell me "tighten fuel cap" almost every time while driving. I got the cap changed, and still the same thing. I took it to the dealer, and they said they scanned it and didn't find anything (when it was under warranty), and told me that's normal (?). And a couple of days ago, the dealer contacted me about a recall for my H2 regarding a defective catalytic converter. I asked them to check the fuel cap issue, but then I changed my mind, thinking that it could have been a problem relating to the Emissions control system (my friend had a Hyundai that gave the same fuel cap/check engine problem, and it turned out that there was a loose hose somewhere around the Emission control system). Anyways, while driving a couple of days after the catalytic converter repair, it told me again to check the gas cap. So, what do you guys think?

Also, I tried putting acetone once or twice in the gas tank to get better mileage, but it didn't work. Could that have contributed to the problem? I got the issue a long time after doing that, though. I disconnect the battery every now and then to reset the computer to clear the check engine light.

So does anyone know anything about this issue?
Any help is greatly appreciated because I'm pulling my hair out from this right now.

Thanks!