gas cap & check engine light problems... - Chevrolet Forum - Chevy Enthusiasts Forums

gas cap & check engine light problems...

Old  August 2nd, 2012, 3:19 PM
gas cap & check engine light problems...

I have a 2005 Tahoe. I filled gas tank up, drove 30 miles, parked it, and when I cranked it back up the check engine light came on and the warning to tighten my gas cap came on. So I did, and sure enough I had not tightened the gas cap. Drove 30 miles back home and light was still on so drove it a couple more days and it never went off. So took it to Auto Zone and they hooked it up and said the code stated it was the gas cap. So bought new gas cap from them. Put it on, light never went off. Took it to mechanic and he said same thing, code was showing the gas cap was the problem. So went and ordered one from the dealership. Put it on, light stayed on. Took back to mechanic, he reset computer and put a ring in the cap just to make sure it was sealing good. Drove for a few days then light came back on. Mechanic guy said it would not hurt the vehicle to drive it, so I did. The light would go off at times and come back on at times but still is on now. Then time for inspection so I had to get it fixed, won't pass because darned light. So it is now at the mechanic shop and the code they get is still that it is the gas cap. They ran the smoke in it and found no leaks at all. They have checked everything and are finding nothing wrong. Man said he has never ran into an issue such as this before and is still trying to figure out the problem. Does anyone have a clue what else this could be?

Old  August 2nd, 2012, 8:04 PM
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Reset the light and immediately get it inspected.

Old  August 2nd, 2012, 9:25 PM
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Take it to a better mechanic. There is no code that says "The gas cap is bad". It could be a possible fix for a code or two but obviously not yours. Autozone parts people are not mechanics, the code never tells you what is wrong it only tells you where to start looking. Autozone"s code reader also only tells you what parts are needed based on probability. What is the code number? Just because that guy has a smoke machine it does not mean he knows how to use it. He must close the vent valve with a scanner or a 12v power source, did he? I have seen Evap codes set for something as simple as spider webs in the vent line. Someone must take the code number then print out the trouble tree and run it down. Just because a guy has a tool box and tools does not mean he can diagnose problems. There are less guys that truly know how the systems in a car work (truly work) then you can imagine.

Old  March 17th, 2013, 11:52 AM
My wife's 2005 suburban has this same issue. I also occasionally get a vacuum leak warning too, but I was told that it comes from a bad seal from the gas cap. I ordered a new cap as well, but it hasn't come in yet. I'm guessing it probably won't fix it though......

Old  March 17th, 2013, 3:03 PM
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without more info can't help much but im assuming you're getting the gross leak/no flow or large leak codes if people are telling you to get a gas cap, which honestly i have only replaced about 2 gas caps compared to countless other leaking parts of the evap system.

post the code and get it smoked tested otherwise its a guessing game

Old  December 15th, 2014, 5:56 PM
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Prime example of someone not knowing what they are talking about. Ther very much is a code in Chevys that says check gas cap.

Old  December 15th, 2014, 8:13 PM
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post the code then. not a dic message but the actual dtc.

I have only seen what was described....a small or gross evap dtc that has you check the gas cap along with other potential faults. Without the proper evap adapter, the gas cap and filler neck cannot be smoke tested correctly.

Old  December 25th, 2014, 11:12 PM
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Gas cap / check engine light

I have a 2009 Silverado with the exact same problem. The Auto Zone guy said to clean the gas cap and filler neck and that would probably take care of the problem. I cleaned them both, but it did no good. I went to the dealer and got a new gas cap and that didn't do any good either. He said they would have to do a smoke test to find the problem. From what I hear, that is very expensive. I don't think there is any code that tells that the problem is the gas cap, only a code that tells the mechanic where to begin. Replacing the gas cap is the cheapest thing to try 1st. The dealer said the evaporative solenoid on top of the fuel tank was the next thing to check, but I don't want to shotgun expensive parts so I need to find a knowledgeable independent mechanic who can trouble shoot this problem and fix it without draining my wallet.


Old  December 26th, 2014, 8:45 AM
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your dealer was correct. evap vent solenoids are common faults. They can be diagnosed in seconds with a bi-directional scan tool. If you don't hear them click open and closed when cycled on and off; they need to be replaced.

if you know what your doing, you can cycle them off and on just by providing a grd source.

Old  December 26th, 2014, 11:39 PM
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Evaporative solenoid testing

Hi Tech 2: It would be appreciated if you would elaborate more on exactly what to ground out on that evaporative solenoid without burning anything up. I have a car lift and have good mechanical and electrical skills, so I don't think it would be too hard to do. It sounds like either the body of the solenoid or a ground circuit wire must grounded for the solenoid to cycle thus simulating the operation of the system.

Thanks, Harv

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