P0446 CODE

2002 Toyota Corolla

Engine Mechanical problem
2002 Toyota Corolla 4 cyl Front Wheel Drive Automatic 114, 00 miles

You have helped me solve problems with my vehicles. Now I need your help to solve a problem with a friend's vehicle. He is short on funds, knows nothing about cars, so I'm hoping I can fix ift for him. His engine light came on and with my scan tool, the code P0446 was listed as the causitive factor. I found out that the P0446 code corosponds to the evaporative emission control system vent control circuit malfunction. A person told me that this code relates to the canister shut valve and that I should replace the canister as well.I went to a local Toyota dealer and the most information I could obtain from them is that four different valves that relate to this code; however, one is the canister assembly that has the shut valve. I believe that I have located the canister by the fuel tank. I would appreciate any information( and diagrams as he does not have any repair manuals) you can give me so that I can repair his Toyota
December 18, 2009.

Hello -

To better assist you is the model a CE, LE or S and what is the engine size in liter?

Dec 18, 2009.
The car is a Corolla CE. The only thing written on the engine is 16V VVT-I. I cannot find anything that lists the engine displacement. I hope this is enough information.

Dec 19, 2009.
Hello -

Thanks for the info.......

I show this code can be one of several things.

Circuit Description

Vapor pressure sensor, canister closed valve Vacuum Switching Valve (VSV) and pressure switching valve VSV are used to detect faults in EVAP system. DTC is set if EVAP system leak is detected or if there is a malfunction in EVAP VSV, vapor pressure sensor VSV or in vapor pressure sensor. Possible causes are:

" Damaged, disconnected or blocked vacuum hose(s).
" Fuel tank cap is installed incorrectly.
" Defective fuel tank cap.
" Vapor pressure sensor circuit is open or shorted.
" Defective vapor pressure sensor.
" EVAP VSV circuit is open or shorted.
" Defective EVAP VSV.
" Canister closed valve VSV circuit is open or shorted.
" Defective canister closed valve VSV.
" Pressure switching valve VSV circuit is open or shorted.
" Defective pressure switching valve VSV.
" Damaged fuel tank.
" Defective charcoal canister.
" Fuel tank overfill valve cracked or damaged.
" Defective ECM.

Is the vehicle running rough, bad in any way or just threw the code?

If it is running basically okay, then this is my suggestion especially since short of funds.

Check all of the vacuum hoses really good. Especially the small ones and areas of sharp bends, sitting against something that could chafe etc, look at the area that it connects to for brittle and splits. I have attached 3 pic below to assist.

Next, I would replace the fuel cap.

Then clear the codes and drive it and see what you find.

It may be the canister etc.........but, when looking at the chart above I would start with the most probable and work my way down. Most of the time I have found either a defective hose or mostly the fuel cap.

Dec 19, 2009.
Thanks for all the information and great diagrams. I forgot to mention that I had him replace the gas cap and I reset the code. It lasted about a week until the light came on again with the same code. The vehicle runs fine with the exception of the light staying on. I will look at the hoses( the pictures will be very helpful) next and report back.

Dec 20, 2009.
Hello -

Thanks for the additional info. Lord willing it is something simple and you will spot it looking around, say a split hose etc.

Also, I am sure you did but want to make sure we are on the same page. We have see where how the gas cap connects, there isn't a good seal. That is, rub your finger around the lip and threads for anything that may prevent a good seal. Some have been slightly bent, or nicked from the fuel hose being put in and prevented a proper seal of the cap.

Good luck and will be waiting to see what you found so the other reader and us too can gain the benefit.

Have a great Christmas if we don't speak again.

Dec 20, 2009.
I apologize for taking so long to get back to you, but I could not coordinate my schedule with my friend's to look at his car. On Sunday I was finally able to inspect all the hoses that you diagramed for me and all appeared to be in very good condition.
Please let me know what my next step should be. If I should replace the canister/valve, how difficult will it be to remove this from the vehicle.

Thank you!

Jan 13, 2010.

Since ANY of the hoses, or valves in this sytem could be the problem, it would be wise to spend the extra money to test the system first! Mechanics use a smoke machine to pump 2psi of smoke into the system, where the smoke leaks out, the part is replaced. Throwing parts at it to try and help is a waste of your time, and friends money! Carefully check the gas fill tube, if the upper half is metal, look for pinhole rust on it...ANY hole, even a pinhole will set the code you have. EVAP VSV in engine compartment is more likley the cause than the canister.

Jan 18, 2010.
If this problem is not corrected can it cause any damage to the engine. I am not experiencing any problems in engine performance at this time. I had the code cleared and currently waiting to see if it recurs. Thanks for your great advice.

Apr 9, 2010.
This is a fuel vapor management problem(gas fumes), probably will not cause engine damage, unless too much fuel enters the catalytic converter, not likely.

Apr 10, 2010.
The VSV is very problematic. I've seen two go bad on different cars in my family and a couple from work associates. Bad design and in fact the EPA sued Toyota to extend the warranty on this part.

May 23, 2010.