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Code P0446

I have a 2003 Chevy Impala and the check engine light is on. They told me that I need to have a smoke test run. How much does a smoke test usually cost? Also what could be wrong with the car and how much does it cost to fix each possible problem?

. And why did you not ask who ever said you need a smoke test how much it was. The service place and your location can have a large bearing on the price.

Try replacing the gas cap with a new one, to see if the Check Engine shuts off.


I did they told me that it would vary and didn’t want to give me no incorrect information.

Evap. Emission
Control System – Vent
Control Malfunction
P0446 This DTC will determine if
a restriction is present in the
vent solenoid, vent filler,
vent hose or canister

This is a cut and paste from an AC Delco technical website

I’m not sure you have a leak. I’m leaning towards a restriction, as the text alludes to

One of those components named might be full of dirt, mud, or spider webs

This code can also come from frequently overfilling your gas tank. If you do this, then the problem can clear itself if you simply stop filling at the first click. If you do stop filling at the first click, then I agree with @db4690.

So if it is blocked or has a leak is it worth getting fixed or will more problems stem from this

Until you know the cost of repair only then can you decide if it worth it to you.

Since 1996,(OBDII) you cannot over fill a gas tank where it damages the EVAP system.

Every EVAP system has a refueling control/roll-over/over-fueling valve.

The EPA knew there would be idiots out there that would try to pack gas tanks which would damage the EVAP system. And they also wanted a means to prevent gasoline from leaking from the gas tank in the event of a roll-over.

So they mandated that every EVAP system be protected with what we in the business call a ROOF(Roll-Over/Over-Fueling)valve.

So you can’t over-fill the gas tank anymore.


I don’t disagree with @Tester very often, but this is one thing I do not agree with him on. Modern cars are required to have roll over protection gas tanks, that is in case of a rollover, there are flaps or valves that prevent fuel from escaping out of the gas tank and feeding a fire.

They theoretically should prevent a tank that is overfilled from allowing fuel to enter the canister, however the vibrations and bumps you feel going down the road allows gas to enter the emissions lines and can cause this issue. If you stop overfilling, the canister will dry out and the problem goes away.

Some cars, i.e Subaru’s (new models) can also suck water into the vent lines through a filter. This can happen when you drive through a flooded street or road. 3 or 4" deep is enough on some models. This does not dry out the same way and requires a very expensive repair. I don’t know if your vehicle is prone to this or not.

The evap system is what keeps the gas fumes that reside above the tank from accidentally leaking out into the air and polluting it. It also improves your mpg’s b/c all the gas gets used to propel the car, none leaks out and lost as vapor. It’s a complicated arrangement b/c air has to come in to replace gas that’s burned as you drive, and air and fumes have to have a place to go when the car sits in a parking lot and is heated by the sun which expands the volume of the fumes. And it has to prevent fumes from being pushed out of the tank and into the air when you fill the tank. What they do is push smoke into one spot and look to make sure it comes out in the correct spot somewhere else. If you have a restriction is might not come out at all, or it might come out in the wrong spot b/c of the restriction.

I wouldn’t guess a smoke test would be overly expensive, but if the problem eludes detection, the time it takes to figure a solution may be 3 or 4 hours, that could be in the $500 range. If you can only afford a certain $$ amount, tell them to stop when they reach that amount. You may not get the problem fixed, but at least you’ll still have money for food. If you feel lucky, try a new gas cap.

You can’t over-fill a gas tank anymore.


I read your link. I don’t see where it supports your argument.

Vent/Rollover Valve[8][dead link]

  • It provides a method of controlled escape for gasoline vapors during the refueling process. It has a mechanism which closes the vent in the event the vehicle rolls over, to prevent spilling of VOCs or fuel in general. It also acts as a fill limit.

It seems the explanation is pretty clear.


Just follow your owner’s manual (this for a 2010 Insight):

Picture 1

I believe I referred to this in my previous post and addressed why I think it does not apply to this issue.



Post 10 ish

I believe Tester is trying to say that in newer fuel tank designs if the owner attempts to pump more gas into the tank than allowed, the extra gas will just spill out at the fill nozzle and leak onto the ground, rather than overfilling the tank to the degree doing so would damage the canister. Before that change the owner could overfill the tank so much it would cause liquid gasoline to move into the canister and damage it; i.e. the extra gas would still go into the already overfilled tank, rather than pour out onto the ground.

If you try to over-fill a modern fuel system, the pressure created shuts the nozzle on the gas pump off.

The EPA doesn’t want raw gasoline spilled on the ground either.

That’s why they mandated a rollover/overfueling valve.