04-07-2010, 11:59 AM
I have a 1999 GMC Jimmy. I keep getting the P0446 code. Can anyone tell me exactly what the Evaporative emissions system vent control circuit is and what it does? Your help is greatly appreciated.
04-08-2010, 09:00 PM
The evaporative emission system collects fuel vapor from the fuel tank when the engine is off. It stores the vapors in a charcoal canister located near the rear wheel on the driver side. When the engine is running, the purge solenoid, located on the intake manifold of the engine, and the vent solenoid, located on the frame crossmember near the canister, both open and allow engine vacuum to purge the canister of the vapors, and burn them. P0446 indicates there is a problem in the vent solenoid circuit. Battery voltage is supplied to the solenoid any time the ignition is in the RUN and START positions through the "ENG 1" 10 amp fuse. The ECM determines when to supply ground to the solenoid to activate it.
04-09-2010, 09:18 AM
04-09-2010, 02:25 PM
Most likely you won't notice any difference in the way the engine runs, and it will not harm the vehicle in any way. It can and most likely will, cause fuel vapors to be released to the atmosphere. I am not a green, tree hugging invironmentalist by any means but, capturing the fuel vapors and burning them can improve fuel mileage, ever so slightly, but nonetheless, it will improve it. Do-it-yourself repairs save money only when you can diagnose the problem correctly and repair/replace only what's necessary. Guessing and replacing parts defeats the purpose of do-it-yourself repairs. Without following the diagnostic flow chart to find the root cause, the best that you can hope for is to make an educated guess. In this case, knowing how the system works and past experience does play a part... The canister is filled with granulated charcoal. When the ECM commands for the canister to be purged, engine vacuum is applied to the canister. Particles of charcoal can get sucked into and trapped in the vent valve passage which can hold the valve either open or closed. You can remove the vent valve and check its operation. If the valve is stuck, and if you can clean it so it operates freely, the canister should be replaced to prevent it from happening again. If the vent valve does not operate when battery voltage is applied, chances are just the vent valve needs replacement.
04-09-2010, 04:01 PM
Thanks again old master. This is very helpful. I will have some one check into it for me. Thanks again!
04-09-2010, 05:50 PM
I already had this problem. It's not something important.
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