Bravada PO 446 Code

[JLKINSER1970]

Hey Everybody

My 97 Bravada has been throwing a PO 446 code. I was told it was the Canister Purge Valve Solenoid. I repalced it and a week later the code came back. Any ideas? The gas tank builds up pressure. When I take the gas cap off the gas tank releases pressure. Also at times when I start the engine it is sluggish and acts like it wants to die but then comes out of it. This does not happen all of the time. I have a new fuel pump, gas tank, and gas cap. No pinched lines. Could my problem be the Canister Vent Valve Solenoid ?

John

[Chris Stewart]

Have you checked all the hoses to be sure none are pinched closed?
Have you had the fuel tank down for any reason?

[old_master]

P0446 is indicating a problem in the EVAP canister vent valve circuit, not the purge solenoid. The first link shows the electrical schematic, and the last 3 links are the flow charts to diagnose the problem. If you follow the flow chart exactly as written, you will find the problem.

http://i11.photobucket.com/albums/a1..._schematic.gif
http://i11.photobucket.com/albums/a1...446_DC1of3.gif
http://i11.photobucket.com/albums/a1...446_DC2of3.gif
http://i11.photobucket.com/albums/a1...446_DC3of3.gif

[JLKINSER1970]

Hey Old Master and Chris, just seen the reply. I replaced the tank but that has been several months ago. I looked and couldn't see any pinched lines.
I have noticed that when I remove the gas cap I get a whooosh of release of built up pressure. The pressure is really strong and if I didn't hold the gas cap I bet it could blow it off when I release it. Could this be causing the PO446 code?
Thanks for the links Old Master. I will print them off an use them.

Originally Posted by old_master

P0446 is indicating a problem in the EVAP canister vent valve circuit, not the purge solenoid. The first link shows the electrical schematic, and the last 3 links are the flow charts to diagnose the problem. If you follow the flow chart exactly as written, you will find the problem.

http://i11.photobucket.com/albums/a1..._schematic.gif
http://i11.photobucket.com/albums/a1...446_DC1of3.gif
http://i11.photobucket.com/albums/a1...446_DC2of3.gif
http://i11.photobucket.com/albums/a1...446_DC3of3.gif

[old_master]

Originally Posted by JLKINSER1970

....I have noticed that when I remove the gas cap I get a whooosh of release of built up pressure. The pressure is really strong and if I didn't hold the gas cap I bet it could blow it off when I release it. Could this be causing the PO446 code?

Actually it's the other way around whatever is causing the P0446 is most likely what's causing it to happen.

[Tech II]

Was the whoosh, pressure or sucking?

The diagnostics are useless, without a Tech II and a smoke machine.....

One thing you can try, is remove the vent valve, and blow it out with compressed air.....then reattach and clear code, and hope for the best....otherwise you will need to go to a GM shop for diagnosis....there is a tsb out there to replace the vent valve, bracket and hose....but you have to perform the EVAP test first, to confirm the particular problem......

Basically, you need a Tech II, to observe the pressure sensor......then you use the Tech II to command the vent valve closed and command the purge valve open...this should lower the pressure and be seen on the pressure sensor data(if pressure doesn't drop, then either the purge isn't opening or the vent is not closing)......then you command the purge valve off....now you watch the pressure senor to see that it is stable....if it changes, you have a leak.....then you command the vent valve open, and you should see a pressure change as it opens...if there is none, then there is a blockage or the valve isn't working....

[Chris Stewart]

So the vent is controlled?
To control vapors?

[JLKINSER1970]

Hey guys, I was thinking today. Could it be my Canister Vent Valve Solenoid? The only reason I changed the purge solenoid was because the person at Autozone told me that was causing my PO446 code.

[Tech II]

Did you read post #6?

[old_master]

Originally Posted by Chris Stewart

So the vent is controlled?
To control vapors?

Yes, the vent valve and the purge valve are both closed when the engine is off so fuel vapor cannot escape to the atmosphere. Under certain conditions, when the engine is running, the PCM will open the vent valve and apply a duty cycle to the purge valve which allows the fuel vapor in the canister to be burned by the engine, and "purging" the vapor canister. If the canister is subjected to raw fuel, it needs to be replaced. This can, and does happen when you overfill the tank... when the pump clicks off while refueling, stop adding fuel.

[Chris Stewart]

Thanks again OM.

[JLKINSER1970]

Well I took down the Canister Vent Valve Solenoid today. I blew in the end of it and could not get any air to go through. Just blew my cheeks up. I was reading on the forum if the Canister Vent Valve Solenoid is bad you can't get any air into it by breathing into it. The new one I could so I replaced it. HOPEFULLY this will fix the PO446 code. It usually takes about a week for it to come on once I trun it off. I will keep you all posted.
Tec II, I did see your post. Thank you very much for the information. I hope this does not come by as an insult because I don't intend it to be but alot of us on here, from my understanding, are amatures and are trying to fix issuse with our vehicles with out going to GM. Now I know sometimes we have too but most of the time we don't like too. They are too expensive and usually try to fix things that don't need fixed. I have had a few bad experiences with GM workshops and one time even had to call GM to get involved to fix the problem. One other time I had to get a lawyer involved to get GM to fix the crank issue I had on an engine with a warranty still in effect and crank bearings that went bad. So taking anything to the shop is the last resort for me. Not saying I won't becxause sometimes I just have too. Hope I didn't offend anyone here.

[Chris Stewart]

Good work, I guess we'll see how things go...thanks.

[JLKINSER1970]

Well several weeks have passed and the code has not come back as of this date. Looks like (fingers crossed) it fixed my problem. Thank you every one for your input!!