Rick's Free Auto Repair Advice

P0446

P0446 Evaporative Emission Control System Vent Control Circuit Malfunction

If you have a P0446 Evaporative Emission Control System Vent Control Circuit Malfunction read this article to fix it. The evaporative emission control system checks to make sure there are no leaks in the lines that run from the gas tank to the charcoal canister and up to the engine. It also checks to make sure the gas cap is sealing correctly.

When you fill your car with gas, the vapors in the tank get forced into a canister filled with activated charcoal. Also, on a hot day as the gas heats up and vaporizes, those same vapors push into the canister where they’re stored. But the charcoal can only hold so much vapor. At some point it has to be emptied. The emptying process is called “canister purge.” Here’s how it works.

The computer orders a canister purge by powering open a purge solenoid. That opens the vacuum line between the canister and the intake manifold. At the same time, it opens a VENT solenoid. That allows fresh air into the canister. So the engine is literally sucking out the gas vapors and purging the canister with fresh air. The computer has to adapt its fuel strategy to take advantage of all the extra gas vapors coming into the engine.

The computer notices the canister is empty when it detects a leaner condition (all the vapors are used up) and it resumes normal fuel delivery. Some car manufacturers then close the VENT solenoid but leave the PURGE solenoid open. That creates a vacuum throughout the entire fuel storage system. Once the correct vacuum is reached, it closed the PURGE solenoid and waits to see if the vacuum holds. If it doesnt, the system passes the test. If it detects a leak, it sets a code.

The computer also watches the electrical activity during the testing process. When the computer operates the solenoids, it sees a voltage drop on the line. If it doesn’t see a voltage drop, it knows there’s a problem with the electrical–either the wiring is broken, or the solenoid isn’t working. In this partcular code P0446, the computer has detected an electrical problem with the VENT solenoid.

To learn more about EVAP systems, read this article

For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.

You need a professional shop manual to work on a late model vehicle. And you need access to the latest technical service bulletins so you don’t waste time and money replacing parts that may misbehave due to a manufacturer’s software glitch. Forget about those cheap manuals you find at the auto parts store. They will just lead you astray. Here are the two best online shop manuals around.

Eautorepair.net is really Mitchell On Demand with a consumer style interface.
Get a 1-Month subscription (31 Days) for $16.99, 1-Year (Best Value!) for $25.99, or a    4-Year (Best Value!) for $39.99. I like the wiring diagrams in Eautorepair.net better than the hard-to-read factory diagrams on Alldatadiy. However, Eautorepair.net doesn’t show how to remove trim or door panels. Alldata does.

AlldataDIY.com is simply Alldata with a consumer style interface. They have a different pricing model. But a 1-year subscription for $26.95. Add additional vehicles for $16.95 for a year. Or, buy their 5-year subscription for $44.95. Add additional vehicles for $29.95 for five years.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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