446 - Evap Engine Light - 2001 Corolla - Toyota Corolla, Chevy Prizm (1998-2008)

Matt (fishexpo) wrote: EVAP problems are the most common ones for our years (1998-2002)- usual suspects are VSV, charcoal canister, and purge valves. Most are close to the tank. Sometimes a EVAP code is triggered by a bad catalytic converter - but usually you'll get a trouble code showing fuel trend issues as well. Bad grounds in sensors also causes issues - but those are generally much harder to find in an intermittent issue, unless you have some circuit that is completely shorted out. Sometimes these problems go away on their own or are fixed while checking on other components.
The same fault codes (e.g. PO 441, and PO 446) can cover anything from a bad gas cap to cracked or leaky vacuum lines to a flooded or cracked charcoal canister. If it is definitely the canister - you should be able to pick one up anywhere from $150 to $250 brand new. Getting to the canister could be an ordeal - it is tucked next the gas tank right next to the rear subframe.

Now I read this from the faq. I recently (Nov) bought this 01 (85,000 miles). When I first looked at it and scanned it had zero trouble codes. After a week of deciding if I wanted to buy it (from brother) the engine light came on and I purchased it anyways. I got the thing scanned and it is the 446 code error for EVAP. I did notice that after driving it for a month the light went off for about two weeks. It then came back and has not gone off again. One other thing to note is that the gas mileage runs about 25mpg. Doesn't this seem low?

Any suggestions or ideas would be great I'm getting ready to take it on a long trip and would feel better having this resolved first.

Most of the EVAP related codes are more of an emissions nuisance than a drivability problem with the 8th gen Corollas - don't let that get in the way a trip. I've done a run from North Carolina to Ohio and back - with my P0440/P0441/P0446 set - no problems at all. As for potential fix - really depends on the history of the car, especially if the code has popped up before and has the gas tank been topped off or overfilled.

Overfilling the tank is surprisingly easy to do - and will definitely cause these EVAP codes to pop up. Pump the gas up until it clicks at the pump or you can stop it before it gets to that point (listen for that telltale "whistling" sound when the fuel gets close to the fill neck. Overfilling can potentially flood the vapor canister with gasoline - if that happens, you have to replace the canister to the tune of $160-$350 for just the part.

Other potential causes for those EVAP codes can be from one of the two main VSVs (vaccum switching valves). One is located near the airbox the other underneath the car by the gas tank, and next to the vapor canister. These valves can get clogged up or gum up due to their relative locations - though it tends to affect the one closest to the vapor canister much more frequently.

Other source are loose or cracked vacuum lines - they run all over the EVAP system and can be tough to find unless you have the right equipment. MAF sensor can sometimes cause an EVAP code to pop up - though this is not as likely as the others.

Unfortunantly, there is NO definite direction that I can point you towards to fix this issue. The EVAP system is quite complex and has multiple potential failure points. Sometimes, a completely unrelated system component can cause the EVAP CEL to get tripped. If you know of a good dealership in the area - might be worth the diagnostic fee to have them check the EVAP system out. I had a local shop do it for me - cost me $85 at the time. Made sure that they actually diagnosed the problem by hand, and not scan the computer. I have a scanned copy of the Toyota FSM procedure in my sig - quite involved process - but the only surefire bet to get that code eliminated for sure. My problem turned out to be a bad check valve at the top of the tank. Others with the same code or family of codes traced their issue to a bad VSV, cracked hose, cracked vapor canister, flooded vapor canister, ECM problem, etc. Basically - no easy answer - but it is "fixable" given enough time.

Overfilling the tank is surprisingly easy to do - and will definitely cause these EVAP codes to pop up. Pump the gas up until it clicks at the pump or you can stop it before it gets to that point (listen for that telltale "whistling" sound when the fuel gets close to the fill neck. Overfilling can potentially flood the vapor canister with gasoline - if that happens, you have to replace the canister to the tune of $160-$350 for just the part.

I have never heard of this. Learn something new all the time. I always fill up my car and fill it up I do. Sometimes I will hear the click and wait a few seconds and do it again so the gas bubbles fall. So as this happened before I took control of the car I could of maybe damaged the canister.

Well even if this isn't the problem it is good to know. I guess my concern is I should probably get it fixed and it is probably just costing me extra in gas to avoid it. More noticable during a long trip. I will check the gas cap as I have read multiple times.

If it is the cap will the light go off again or does it have to be manually cleared?

evap codes are weird. sometimes they will clear ,but a trip to autozone and they will clear it for free. your mileage is not affected at all. this system called the al gore light , it does nothing but put excess gas fumes back into the engine to be burned after they go thru the charcoal canister filter just like a p.c.v. but much more complicated. remember too that a loose gas cap or a worn gasket on a cap will trigger the code too. don't spend a lot of worry or cash for a useless problem. if the dealer says its the canister just wait it out. these canisters dry out and fix themselves sometimes. too expensive to just replace and the mechanics love that job. 1 hour replacement and they charge almost a grand. now if its a cracked line ,thats a different ballgame. only a very well trained mechanic with the right diagnostic equipment will find it . a good independent foreign or domestic auto mechanic can fix it ,but you need to ask if he has a gas fume sniffer to find a leak . that piece of equipment has come down in price a lot the last few years just like an obd2 code reader. any good shop will have both ,but finding it takes a mechanic who has seen the problem before and knows where the wear or pinch points are. you have to ask the right questions ahead of time. i call the shop or stop by and ask to talk to the mechanic directly . ask for their number 1 guy. find out if he has seen the problem on your vehicle . if not go elsewhere. even the dealership guys are not all good. some are just part re placers. my best friend is a number 1 toyota/mazda senior master. he knows all too well about the hierarchy. don't let them b.s. about all our guys are good or well trained. most shops have 1 guy or the owner and a number 1 guy in diagnostics. find him and pick his brain. if they won't let you talk to him go somewhere else. good luck