What does OBDII code P0446 Evaporative emissions control vent circuit low mean?
The previous answer was good for high dust environments (and if you have a Ford Van all environments are to be treated as high dust) but for those of us in high corrosion environments, consider the following: If you have an Explorer (Or Ranger/Mazda B-series) check for a broken wire near the left side framerail near the rear axle If you have a Hyundai (including Kia), Nissan (including Infinity) or Toyota (including Lexus or Scion) you should disconnect the electrical connector and then apply and remove 12V power to the vent solenoid/valve. The difference between 12V applied and not applied should be the difference between not being able to blow through it and being able to. After testing at least 5 times, if it fails even once, replace the solenoid/valve In the case of Nissan or Toyota, if replacing solenoid/valve it is usually best to replace the canister as well as you might inadvertently break the canister while replacing the solenoid/valve.
With many Nissan vehicles, it is almost impossible to not break the canister without using techniques involving unreasonably high fire hazard Answer == Brian==It is probably the gas cap not on tight. Have the codes removed and see if it comes back on after you tighten the cap. GoodluckJoe Well, my experience with a 2000 GMC 3/4 ton truck says otherwise A loose gas cap will not give you P0446 because that is the code for a failed vent test Here's how it works: To check the vent system the engine vacuum valve is opened at the same time as the charcoal filter vent valve is closed.
This creates a vacuum in the gas tank and when the vacuum reaches a certain level, the vacuum valve closes and the vent valve opens and a timer is started. If there is a restriction in the vent valve or it doesn't operate electrically, the tank fails to re-pressurize within the correct time and you get a P0446 Here's what I did: I removed the vent valve and found it choked with a fine dust. I cleaned the valve, but noticed that there was lots of dust in the tube running down to the charcoal cannister and realized the gravel filter in the vent valve is useless at stopping dust.
I took out the cannister and discovered an amazing amount of dust clogging it up. I cleaned the cannister by holding it vent side down and sharply tapping it many, many times it while blowing air (at low pressure) through it toward the vent side until it passed air freely both ways. Did I mention that there was an amazing amount of dust that came out of the cannister?
I would think that gasoline residues from overfilling might clog up the cannister too, but that didn't happen in my case Below are what I consider the possible causes of P0446 in the order of least likelihood (IMO) for a vehicle used in a high dust environment: Electrical vent driver circuit in computer burned out (especially if the vent valve is shorted), electrical vacuum valve driver circuit burnt out, vent valve coil open or shorted, vacuum valve coil open or shorted, bad vacuum sensor in the gas tank, vent valve filter clogged with dust, charcoal cannister clogged with dust or residues Removing and replacing the vent valve and especially the charcoal cannister in a GMC truck is a major, major pain in the a-- because the entire vehicle was carefully engineered by GMC so as to make replacement as difficult as possible. It does no good cleaning and replacing a clogged vent valve as the cannister will be clogged too. A new cannister is about $175, but a cleaned one is free BTW, my vent test works perfectly now Added by Protoart: If you have the P0446 code and the vent valve is bad, don't continue to drive, or you will clog (saturate) the canister with gas for sure My wife's 05 Scion, check engine light w/ P0441,0442, and 0446.......cleared with my scanner, never came back after I tightened the gas cap.
The code P0446 is set when the engine computer recognizes a fault or restriction at the vent control part of the Evaporative emission control system (EVAP). The description of the fault varies between different car manufacturers, but one thing is common, the code P0446 doesn't directly point to a defective part; some testing might be required to pinpoint the faulty component. Read how the EVAP system works below.
A GM technical service bulletin for 1999-2007 Chevrolet Silverado and GMC Sierra describes a problem when if the vehicle is driven in dusty environment, the dust can enter into the canister vent hose and cause restricted air flow that can set the code P0446. The bulletin recommends checking the vent valve assembly and if needed, replacing with an updated part. A Nissan technical service bulletin (TSB) for late 90's Maxima, Sentra and Pathfinder mentions a faulty EVAP system pressure sensor that can cause the trouble code P0446 and some other EVAP system codes.
In many Toyota vehicles including Camry, Corolla, Avalon, RAV4, Tacoma, Tercel, as well as Lexus RX 300, ES 300, SC 400, LS 400 and LX 450 with the code P0446, the repair often involves replacing the EVAP vacuum switching valve (VSV) and charcoal canister as an assembly. In addition, all the involved vacuum hoses need to be cleaned or replaced. A TSB for 1999 Toyota Corolla suggests replacing the ECM with an updated part as a repair for the diagnostic trouble code P0446.
In some GM cars, a bad fuel tank pressure sensor also could cause the code P0446. The vent control valve and vent hose (on the left of the vent control valve in the diagram) need to be checked for blockage; The vent control valve also needs to be tested; the vent control valve is an electrical solenoid/valve that closes when the voltage is applied. Unless an obvious problem is found (e.g. Blockage at the vent control valve), the whole EVAP system might need to be tested with a special testing equipment known as a 'smoke machine'.
A good scan tool with active test capability can also help. Not every auto repair shop has this equipment, you might need to visit a dealer or a larger well-equipped shop for repairs. The Evaporative System (EVAP) prevents the fuel vapors from the fuel tank from escaping into the atmosphere.
The fuel vapors from the fuel tank get trapped in the charcoal canister; the charcoal canister is filled with small pellets of activated charcoal that absorb and store vapors. When the engine is running and other conditions allow, the fuel vapors are purged from the charcoal canister into the engine air intake to be burned (see the diagram). The vent control valve is usually installed at the back of a car or truck; near or at the charcoal canister.
The vent control valve is an electrical solenoid/valve that is controlled by the engine computer (ECM). The vent control valve is normally open; it controls the air supply into the canister. The vent control valve closes when the ECM performs the leak test of the EVAP system.
During the leak test, the ECM seals off the EVAP system by closing both, the vent control valve and the purge control valve (solenoid). Once the EVAP system is sealed, the ECM monitors the vacuum or pressure in the EVAP system. If the EVAP system doesn't hold the vacuum or pressure, the ECM recognizes an EVAP leak.
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