How to test Vent & Purge Valves - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 General Tech Q&A > General

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  #1  
Old 10-31-2010, 11:35 PM
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huronnie huronnie is offline
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How to test Vent & Purge Valves

Hi, this is my first post at this site and I am hoping someone can help. I am getting a P0455 error code which is some type of large vent leak in the EVAP system. I was told to replace the gas cap, and I did but that didn't help. The next thing I inspected was the filler tube hose but havn't removed it yet for a closer visual inspection. But what I would like to know is; is there a way to check that the vent valve and the puge valve are working correctly before I go changing parts?
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  #2  
Old 10-31-2010, 11:41 PM
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Quote:
Originally Posted by huronnie View Post
.....The next thing I inspected was the filler tube hose but havn't removed it yet for a closer visual inspection......
Welcome to the forum.

When you check the filler tube hose, check the metal neck on the tank too....there have been tanks that had the necks cracked open.....GM will replace the tanks.

Can't help on the vent purge & valve.
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  #3  
Old 11-01-2010, 12:28 AM
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I think the GM Tech II tool or a high end scan tool can address each of the valves using the data bus for a test. Otherwise it's a tedious wire tracing and jump wire exercise.

Sometimes, mechanics, and especially dealers, charge more for the diagnostic time than just shotgunning the parts would cost. Not certain in this case, or if you have access to a GM experienced independent mechanic.
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Old 11-01-2010, 12:55 PM
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How to test vent & purge valves

Quote:
Originally Posted by petevw View Post
Welcome to the forum.

When you check the filler tube hose, check the metal neck on the tank too....there have been tanks that had the necks cracked open.....GM will replace the tanks.

Can't help on the vent purge & valve.
Thank you, I will check that out.
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  #5  
Old 11-01-2010, 01:09 PM
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Test vent & Puge valves

Quote:
Originally Posted by the roadie View Post
I think the GM Tech II tool or a high end scan tool can address each of the valves using the data bus for a test. Otherwise it's a tedious wire tracing and jump wire exercise.

Sometimes, mechanics, and especially dealers, charge more for the diagnostic time than just shotgunning the parts would cost. Not certain in this case, or if you have access to a GM experienced independent mechanic.
Yeah, I've been thinking about getting one of those scan tools; Do you know if I can just take off either the vent or puge valves and manually test them by connecting them to a 12 volt source?

I pulled off the vent valve yesterday and it seemed ok only because when I blow into it hard, the ball inside will plug the line so I imagine its controlled by some electro magnet so I'm thinking maybe I could test it by the two wire leads that go to it?
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  #6  
Old 11-01-2010, 01:19 PM
Wex Wex is offline
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Quote:
Originally Posted by the roadie View Post
I think the GM Tech II tool or a high end scan tool can address each of the valves using the data bus for a test.
I bought a cheap Harbor Freight scan tool because it was on sale. It claims to have Evap leak test ability. After purchase I realized that some of the functions were not available to my model year trailblazer.

I do not have the time at the moment, but can see if the test is supported in the morning when I get back.

The scanner was: http://www.harborfreight.com/can-obd...ner-98614.html

It can be had for around 80 if you get it on sale.

The pdf manual is available on that site in the proper tab. Here is a screenshot of a paragraph that is related.


Scanner was incredibly mediocre but I bet you could do a real real easy merchandise return on it.
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  #7  
Old 11-01-2010, 03:21 PM
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How to test vent & purge valve.

Thanks, that would be great to know if it is supported!
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  #8  
Old 11-01-2010, 11:12 PM
Jerryod Jerryod is offline
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I had a similar problem. Mechanic used the GM tech II took 5 minutes to do the test. Determined that it was the Purge valve under the hood near starter.
Replace the valve. Been good now for 2 months.
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  #9  
Old 11-02-2010, 08:42 AM
Wex Wex is offline
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Quote:
Originally Posted by huronnie View Post
Thanks, that would be great to know if it is supported!
I plugged in the device this morning. Made my way through the menus till I found the command. Pressed enter and it said sending command. After about 5 seconds it said hit any key to return to menu.

I am guessing that it is supported and did the leak test. Other tests before on the menu would either say unsupported or fail. I did not hear anything unusual after the test command but I do not know what I am listening for either lol

If you live near a Harbor Freight you could try it and simply return it saying you did not like it. Returns are pretty much no questions asked with receipt.

Knowing what I know now, I would spend the money on a better device. But I am content, I simply kept it for the data logging ability.
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  #10  
Old 11-02-2010, 12:11 PM
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huronnie huronnie is offline
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Thanks for the info! I was looking at the purge valve last night, very difficult to get to. I will pull it off this weekend and see if I can test it. I will also look at the fuel tank neck, someone said that there was a call back on those because of cracking.
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