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Q: P0446 Emission control system vent circuit malfunction

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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?

A: Hello! We will be happy to assist you. It m...

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.

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