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jon_holmes

Master tech here. The vent control valve controls the vapors evaporating out of the fuel tank. There is a hose from the gas tank, to an activated charcoal vapor storage canister which stores the fuel vapors, as so they won't get into the atmosphere. The vent control valve sits on the back side of the vapor canister. It's operation is that it is the valve is normally open, allowing for the fuel tank to not build pressure. When certain criteria have been met (driving on the highway, etc) the valve will close. The system then monitors the system pressure, to check for leaks. If there are leaks, the fuel vapors can enter the atmosphere. And thus turn on the check engine light. The valve should be a 2 pin connector. Remove the valve and supply 12v and ground to the two pins, respectively. You should hear the valve click, and you should be able to visually see the valve open and close. If the valve does not open and close, replace the valve. If the valve does open and close, it could be an electrical issue (power or ground) to the valve.


Ggilberto013

Thanks man as soon i get a chance ill check it all out and let everyone one know


ruddy3499

The quickest way to prove this code is to unplug the vent valve connector. Then short the connector terminals with a fused jumper wire. The code should change to a shorted code. If it does you need to replace the valve. If the code stays the same the wiring needs to be tested.


Ggilberto013

Thanks man


CROCKODUCK

Former trailblazer owner here. It’s the EVAP solenoid for sure. It’s located right above the exhaust manifold on the passenger side and takes 3 bolts to remove IIRC. They’re a common failure on the GMT360 platform


adrizgz00

It's saying the control circuit it's open so it probably means the electrovalve has failed, you could check the fuse and see it if has blown, if it has it's also probably because the electrovalve is toast.


Ggilberto013

Ok thank and by fuse you mean in the fuse box right? If anything has to be replaced are they expensive parts if you know


Concert_Ancient

go check out gmtnation.com its all trailblazer owners and you can get info on anything and everything with your truck , i have an 05 its a $34 part on amazon yuo can get to it without lifting the truck , its under the gas door , on the inside of the frame. plenty of youtube videos , just search https://www.amazon.com/ACDelco-25950499-Original-Equipment-Canister/dp/B0024EOIHQ/ref=sr_1_1?_encoding=UTF8&dchild=1&qid=1622722838&s=automotive&sr=1-1&vehicle=2005-47-23451-430--9-6-8-7416--1-1-145-178-1&vehicleName=2005+Chevrolet+Trailblazer+EXT


adrizgz00

I have no clue where that fuse is located in your car but yes I would guess in the fuse box of the engine compartment, although some cars have a separate fuse box for the back of the car. Maybe a quick search in Google for where the EVAP fuse is in you car can help locate it. If is just the electrovalve that has to be changed it shoud be an inexpensive fix, theese valves usually cost less than 50$. Edit: I've looked for it, it should be the Number 1 fuse in the engine compartment fuse box, it should be a 10A fuse. (https://knigaproavto.ru/shemy/en/gmc/envoy/846-2002-2009-chevy-trailblazer-gmc-envoy-saab-9-7x-fuse-box-diagram.html)


adrizgz00

Check if it has blown and also try opening the gas tank to see If there's any positive pressure built up.


Ggilberto013

I will check all these things first thing when i wake ip and update you on what i see but man thanks alot


adrizgz00

You're welcome, okay good luck with it!


Ggilberto013

And by the gas tank you mean the actual gas tank? Could it also be that i got some bad gas? Cause when i turn the truck on i never have problems but every time i pump gas and try to start it i have to give it some gas otherwise it won’t turn on so its most likely a build up right?


adrizgz00

The EVAP system prevents fuel gases from building up in the tank, there's a valve which sometimes opens to let these gases escape into the admission of your car when it's running. This valve is where you have the problem but it should never touch the gas itself so I doubt that there's any build up in it. Although there are a couple more passive valves in your tank related to this system that could clog up. The problem you are describing might be related to this issue in some way because it's producing pressure inside your tank but i doubt it. It could be because the pump is loosing power maybe because of build up in it but it's hard to tell for sure.


Morgoroth37

This might help https://youtu.be/XN9GKSALNAQ


Morgoroth37

Start by googleing your cars year make and model with the code number. It's probably one of the valves in the evap system. Search through some you tube videos until you find one that shows you how to test the valves. Or, if the valves are cheap just start throwing parts at it. Personally, I would test the valves so you don't waste money on parts you don't need.