# Pressure build-up in the gas tank



## scottyknows50 (Feb 19, 2010)

I have a 2000 2500 Silverado. There has always been a "woosh" of air when I unscrew the gas cap. Anyone know what the cause of this is? My SES light came on today, I put some gas in, and soon after the SES light went off. Is this pressure causing a sensor to trigger? Thanks.


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## RepoMan207 (Oct 7, 2008)

That typically happens when you run your tank low on gas. The vapors build up. It also happens when one drives very erratically with low fuel levels. Typically, I think it has to be in warm weather as well.


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## Holland (Aug 18, 2010)

Is the air "whoosh"-ing in or out of the tank?


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## scottyknows50 (Feb 19, 2010)

well, it's been about 35-50 degrees here this past week and i'm not sure if the air is rushing in or out, i will have to feel with my hand next time i drive it. SES light came on AGAIN today after about a 10 minute drive. it seems to always do this- if i have an eighth of a tank or over half.


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## RepoMan207 (Oct 7, 2008)

Maybe your vent side is plugged up?


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## Flipper (Nov 1, 2001)

Try replacing the gas cap.


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## 496 BB (Feb 11, 2010)

Check the code at Auto Zone.


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## Philbilly2 (Aug 25, 2007)

Somone told me once that it is because your vent is plugged.


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## flykelley (Dec 29, 2003)

Vents being pluged is a common problem, are you having a hard time putting gas in the tank? When mine vent was plugged I had a hard time putting $10.00 worth of gas in the tank. Chevy makes a kit to relocate the vent tube.

Regards Mike


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## scottyknows50 (Feb 19, 2010)

where is the vent and how can i "unplug" it?


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## Holland (Aug 18, 2010)

Get your truck hooked to a scan tool before you start unhooking stuff. Even if you can just get the code number. I have alldata i can look it up for you.


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## scottyknows50 (Feb 19, 2010)

ok, i will see if advanced auto parts has a code reader. i don't have an autozone nearby.


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## scottyknows50 (Feb 19, 2010)

I scanned the truck today and the codes said O2 sensors (both?) and Throttle Position Sensor. The code reader also said after every one "circuit malfunction"- anyone know what this means?? The guy at the auto parts store didn't. The truck is acting weirder as time goes on. My tranny has started to shift quite abruptly. I'm not sure if it just happens to be happening now, or if somehow something isn't getting enough power- I guess I'm lost. Thanks for any help.


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## Holland (Aug 18, 2010)

Do you have the actual codes? Would make things alot easier.


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## stacks04 (Jan 22, 2008)

Sometimes when a ses light is on because a sensor is not providing the ecm with a reading or giving an improper reading the ecm will default to known values for things like shifts and fuel distribution. This could cause the vehicle to react differently than if it had the proper readings. It is a failsafe that the ecm has so in the event of a single electrical failure you will be able to still drive the vehicle, preferably to a repair shop. O2 codes will hurt fuel economy but not usually anything else. Probably a o2 heater code.


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## Reliable Snow and Ice (Dec 22, 2009)

could also be cataliac converter being plugged up


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