P0446 Code (Causes, Symptoms, and How to Fix)

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All vehicles have an evaporative emission control (EVAP) system specifically designed to prevent releasing toxins into the air. When you put your gas cap back on, it traps the fuel and its toxins inside.

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Fuel vapors go through a vent line into a charcoal canister, where activated charcoal absorbs some of the fumes. The electronic control module (ECM) then allows the vent valve to push the fumes into the engine air intake.

Vapors travel to the engine air intake through the purge valve. Once there, they mix with air and fuel, creating the combustion that powers vehicles. If the vent control valve doesn’t work, it triggers the P0446 code.

What Does Code P0446 Mean?

OBD-II Trouble Code P0446 Description
Evaporative Emission Control System Vent Control Circuit Malfunction

The vent control valve and the purge valve make the EVAP system work. The vent control valve keeps the system moving by pulling fumes in, then pushing them out through the purge valve.

The purge valve acts as the exit to the engine air intake. The only way fumes can get through the purge valve is if the ECM tells the vent control valve to let air through. The P0446 code appears when the vent control valve experiences a malfunction.

These issues appear during the ECM’s regular testing. When the vehicle isn’t running, it tests the EVAP system for leaks by closing the vent control valve. Closing the valve seals the EVAP system off completely, and no air or fumes should escape.

If the vent control valve cannot maintain enough pressure to seal the EVAP system, it triggers the P0446 code.

See Also: Code P0456 (EVAP System – Small Leak Detected)

Symptoms of Code P0446

The P0446 code produces three primary symptoms. The first and most conspicuous symptom is a check engine light.

Second, look for a decrease in your vehicle’s fuel economy. If you find yourself heading to the gas station more frequently, you might want to get a diagnostics check-up.

Third, you may notice a gasoline odor. Since the vent control valve can’t seal itself, the fumes can escape and create a fuel smell around your vehicle. Inhaling these gas fumes can be dangerous to your health.

Causes of Code P0446

A broken, damaged, or improperly installed gas cap most commonly raises the P0446 code. However, other, less common causes can also arise. They include:

  • Vent control valve: Without a working vent control valve, two things could happen. A faulty vent control valve can seal the fumes inside with nothing to move them, or the vent control valve can’t maintain enough pressure to keep seal the vapors in at all.
  • Fuel tank filler neck: If the fuel tank filler neck has a crack, pressure can’t hold. The crack will undermine the pressure from the vent control valve. The fuel tank filler neck may also be distorted or damaged in another way to creat the same effect.
  • EVAP system hoses: Pressure can also leak from the hoses in the EVAP system. A smoke test can diagnose this issue.
  • Fuel sending unit gasket or seal: This gasket or seal ensures that the fuel stays in the unit and doesn’t drift elsewhere in the vehicle. Even if fuel doesn’t leak, the pressure may weaken.
  • Charcoal canister: This can split or become damaged. As the main component that holds fumes, the charcoal canister crucial to the EVAP system.
  • Fuel tank: The fuel tank can cause the P0446 code to display, as the fuel tank feeds the EVAP system.
  • Electrical connections: Vehicles run on electrical connections, just like computer. A shorted or open electrical connection affects the EVAP system.

Is Code P0446 Serious?

The P0446 code won’t put you in any immediate danger. You can still drive your vehicle if you see this code. Other than the check engine light, you may experience reduced fuel economy.

While this code may not create life-threatening problems, anything that triggers a check engine light deserves attention.

How to Fix

To fix code P0446, you should first inspect the gas cap. EVAP system issues have many potential causes, making them more difficult to diagnose. Taking a progressive approach from least to most severe is most efficient.

If the gas cap is faulty, damaged, or deteriorating, replace it and then clear the code. If the P0446 code persists, check for a leak. Some mechanics use a smoke test to check for leaks. A smoke test pushes smoke through the EVAP system to see if the smoke exposes any leaks. After you repair the holes (if you find any), clear the code.

The next move is to check the EVAP controls. They could be sticky, clogged, or have an internal solenoid failure. There are several ways to check the controls. Try blowing through the vent control valve. If it doesn’t open, it may be sticky or clogged.

Replace any damaged parts, clean the pieces already there, and check for the P0446 code again.

 

Comments

  1. The gear of my vw Passat refuse to select,what could be the problem,it only show D at dash board, put it through others even at park is not showing and the reverse gear is working with difficulty

    Reply
  2. I have a 2001 toyota 4 runner, I have replaced both o2 sensors, cat converter, mass air flow, map sensor, had to take the exhaust off but I have a straight pipe in its place, replaced the spark plugs and wires, the evap canister (charcoal canister) checks the hoses under the hood, the lines under the truck are getting there but not leaking yet, I did notice that there was a broken piece of the canister to 1 of the hoses and I fixed that piece & rigged my own replacement piece, changed the oil and filter, changed the transmission fluid, pan and seal, I am going to be replacing 2 of the rubber fuel hose this afternoon as when I checked these 2 hoses they were corroaded, & I will also be attempting my own exhaust pipe replacement as I dont like how I have it now, but I think I will stick with a straight piping instead of the swirls piping for easy access, anyway i still dont have the pick up & go like i used too, it hesitates on acceleration & i dont know what else to do. I feel like I’ve dont mostly everything and knowing my luck its something stupid & cheap but i dont like taking my truck in to the dealership as they used to take advantage since I’m a female & lied to me on several different occasions about them fixing the issues and charging me for them when in fact nothing was fixed at all. Female or not, doesn’t give them the right to do the **** they have, so I have learned how to do the work on my truck with youtube, my best friend who has his own shop but lives a ways away & reading all that I can b4 doing the work as well as having the manual and my father when in doubt. I am really low on funds, especially now, I have no job & 4 kids to feed by myself. I need help getting my truck working * running properly, PLEASE HELP, if u have any suggestions or what I can look at next or check or test cause I’m at a lose, even the injectors are ok. Maybe it’s just time I get a newer vehicle but who can afford another Bill’s especially a new car PYMT. The codes range from p0172, p0440, p0171, to fuel system to rich, emissions system, evap system malfunctions, I feel like I’ve dealt with every single code there is & I should have a brand new running vehicle with everything that’s been replaced on it but I dont. I bet I’ll probably have to drop the gas tank & replace all of that as well along with the axels bearings, drive shaft I’ve done, I love my truck, u cant go wrong with a toyota 4 runner 3.4 liter v6 which is the better engine that toyota built & they will run forever, well maybe not mine but I cant put her down just yet, shes my beast help me fix my beast.

    Thank you very much, I appreciate all the comments that I can get in response to fixing my purple beast.

    Sincerely,
    Olivia De Tienne

    Reply
    • The amount of DIY work you’ve done on your rig is admirable! I think you may save money in the long run by bringing your vehicle to an independent mechanic for a formal diagnosis. Independent mechanics are almost always cheaper than dealerships. Ask around for trustworthy shops in your area.

      After the shop diagnoses the issue, they don’t have to replace the part if you don’t want them to, but having that professional diagnosis may end up being cheaper and less frustrating than throwing parts at the problem. It could be a simple fix such as an O2 sensor, open circuit, clogged hose, etc. If this is the case and you fix it yourself, it’ll probably only cost you a few bucks over the diagnostic price, which ranges from $100-300 depending on how in-depth they go.

      If you have the time and the patience, you could also read through the fuel system section of the factory manual like a novel and perform the diagnosis yourself using the recommended procedures. It’ll take quite a while to learn the ins and outs of the system (it’s pretty complicated), but you’ll save even more money that way.

      Reply

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