Check Gas Cap

[Awais Bokhari]

Folks,
I recently bought Montana SV6, 2005. The issue I am facing is everytime I fill up, as the gas bar goes down by about a notch I get "Check Gas Cap". I have rotated the gas cap a number of times to no avail. If I ignore it, it is followed by "Check Engione Light", which continues to bother me. I took it back to the dealer where he hooked up and cleared the light, with his diagnostic computer, saying always rotate your gas cap two turns after installation. I have been doing it every time I fill but to no avail.
Any corrective suggestion?

[JabbaTHutt]

Quite interesting what they can do with a computer now adays.

I would go to the local parts store and purchase a new gas cap and see if that cures the problem.

If a gas cap doesn't seal the system when it is checked in an etest it will fail the etest if everything esle checks good, maybe the computer in your van can tell the cap is not sealing the system and that is what it is supposed to be telling you.?

[hufhouse]

There is a very complex test that occurs to make sure that your fuel system is a "closed loop", not allowing any vapors to escape. It involves a couple of solenoid valves and a sensor that checks for proper pressure. Essentially, it puts a vacuum of a certain amount on the gas tank, and it must be able to hold that vacuum for a set time or the test fails.

On most cars, this test is run once a trip when your car is warmed up. There are some other variables, too, like how much fuel is in the tank.

I'm guessing that you get the "gas cap" message if it fails once, since that is the most common reason for the test to fail. Most cars don't have the "gas cap" message and the driver just gets the dreaded Check Engine light. If the test fails again, it must go to the Check Engine on the Montana.

If I'm guessing right, that's a really good design. So many people pay $79.95 to have a mechanic tell them their gas cap wasn't on tightly.

You can try a new gas cap. It's certainly possible that the gas cap is bad. However, it could also be one of those solenoids or a sensor. If the new gas cap doesn't fix it, you'll need to go to a mechanic with advanced diagnostics who will be able to run the test manually and see what is failing.

I really doubt that it would be something terribly serious, like a hole in the filler neck or a fuel line. You would be smelling gas if that was the case.