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!

 

Replace gas cap...if that doesnt work run a smoke machine through it..

 

I already replaced the gas cap. What do you mean by running a smoke machine through it?

 

Most shops can actually pump smoke through the system to determine if there is a leak. it makes it easier to track down the leak in your system.

 

Hello everyone

I would look at leakproofness of tubes of ventilation of a tank

 

Oh ok I will try to get a shop to do that

 

So, could it be just a loose hose under the car or something along those lines?

 

Yes it is correct

 

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

 

EVAP system