Q: P0446 Emission control system vent circuit malfunction

asked by on June 24, 2016

The check engine light came on three weeks ago. I went to get the code read and it say “P0446 - Emission control system vent circuit malfunction.” After clearing the code, a couple of days later it came back on. After this, I took my car to a mechanic who told me that the problem was a bad rubber gasket on the gas cap. It looked smashed to me. After that, I purchased a stant cap. Three weeks later - the light came back on. I noticed that the new rubber gasket looked loose and wasn’t sticking to the cap. I asked the mechanic about it and he found one in his shop and said to try it (a Honda gas cap). In your professional opinion: is the gas cap the problem, should I try the Honda gas cap, or is it something else and what should I do?

Hello! We will be happy to assist you. It may be the gas cap because one way the EVAP system tests itself is by monitoring the pressure inside to fuel tank and comparing it to atmospheric conditions. If the pressure inside the tank is equal to atmospheric pressure code P0446 will set.

Being that you replaced the cap and it didn’t solve the problem I believe the problem is elsewhere, unless the gas cap is defective. If the seal looks questionable as you say it would be a good idea to return it for another one. I wouldn’t try the Honda gas cap.

I strongly believe that the problem is with the EVAP canister or the EVAP vent solenoid. Both are likely causes of code P0446 on your particular make and model. Have a technician test the solenoid to ensure it actuates properly. Also test the EVAP canister by using a smoke machine. If the smoke escapes through the canister the canister is bad.

If you need assistance with these checks, contact a certified technician to diagnose your Check Engine Light and repair your vehicle.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

Bad engine knock, what can I do?
The 2007 Ford Fusion 2.3l Duratec is usually a very dependable engine with few problems. However, there are several issues that could cause knocking and engine seizure. The engine oil filter in this engine is a cartridge type that has...
How Does My Car Monitor Tire Pressure?
All of the cars built today come equipped with a tire pressure monitoring system (TPMS) (https://www.yourmechanic.com/article/how-does-my-car-monitor-tire-pressure). This did not become a requirement until about 2006. At that time, it was determined that a vehicle can be much safer if the...
Not sure if I messed up my engine
Hello Sir, From the symptoms you describe it would not appear to me that you have messed up your engine. Usually a Check Engine Light (https://www.yourmechanic.com/article/the-check-engine-light-demystified) that is flashing means that there is a problem with the vehicle that is...
my battery keeps going dead with a new alternator and new battery
Hello, thanks for writing in about your Oldsmobile 98. You need to have the charging system checked to see if the alternator (https://www.yourmechanic.com/services/alternator-replacement) is charging the battery. You may have a blown main fuse (https://www.yourmechanic.com/services/fuse-replacement) if the alternator is proven...
I was driving down the road just fine all of a sudden my battery light came on for a second then all of my lights came on and then
Hello. Obviously, there's an electrical issue (https://www.yourmechanic.com/services/electrical-components-are-not-working-inspection). To rule out the simple and obvious possibilities have the battery load tested at a major, reputable battery store (this is a common test; they have the tester) to be sure the battery...
Starting problems - 2004 Lexus LS430
Hi there. This sounds like a case of a failed alternator & battery duet. Many times these can fail within close time frames of each other and are usually recommended to be replaced together so that it has a new...
Harsh ride over potholes
Hi there: In general, OEM parts are designed to maximize comfort and tend to wear out sooner than they really should. This is why OEM tires wear out so quickly. Aftermarket parts (https://www.yourmechanic.com/article/is-an-aftermarket-car-part-as-good-as-an-oem-car-part-by-brady-klopfer) (in general) are designed to maximize performance...
Car makes a long thumping noise and skids once the brake is applied
Hello. Does the noise and slipping seem like it is coming from all wheels? It is likely that the brake pads have been installed improperly on all or some of the wheels. The pads can be in crooked, or faulty....
If my car leaks oil and if i use synthetic will it leak more
The consensus in the industry does seem to be that existing leaks will leak more, to some degree, with the use of synthetic oil. This is ONLY the case if you have existing leaks and how much more of a...

Related articles

What Causes a Car to Overheat?
Several problems can make your car overheat. A leaky cooling system, blocked radiator, bad thermostat, or failed water pump are common causes.
A Buyer’s Guide to the 2012 Chevrolet Malibu
While While many people thought that Toyota and Honda had taken over the mid-size family sedan market with models like the Camry and the Accord, Chevrolet surprised the whole market with the Malibu. Available with either a four- our six-cylinder...
What Does the Parking Assist Indicator Light Mean?
A parking assist system helps your car park when it may be tricky to do so. If the light is flashing, dirt may be blocking the sensors from working.