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Evap control errors

Ahoy all,

For a few years now, my 2005 Corolla has been making a pretty loud brief swooshing noise when starting in the morning, if the night was particularly cold. It would start normally, so the noise was just an annoyance. When the weather is warm, there’s no noise.
Not sure if it is related to the story above, but a few weeks ago along with this swoosh the check engine light went on with codes P0441 and P0455. The local mechanic said it’s probably the gas cap and cleared the errors, after which all was well temporarily. A few days back, it got pretty cold here (i am in CO) and the light is back on. This time, in addition to the error codes above, we have two P0456. The mechanic did the diagnostics (or said he did) and came back with an estimate for replacing the evap control canister (the part itself priced at $420). I know it’s impossible for you to diagnose anything based on my post, but do you have any suggestions? Is it definitely the canister and not something else, something possibly cheaper, like a hose? Having read a bit about this stuff, I can definitely say that there is no fuel smell in the cabin or a fuel tank leak.

Your thoughts are highly appreciated!

All of those codes do point toward a problem with the evaporative emissions system, but the carbon canister might not be the source of the problem.

The problem could possibly relate to a deteriorated gasket on the gas cap, and the solution could be as simple as replacing the cap. Have you taken a close look at that gasket?
Or, there could be a leak in one of the hoses associated with the evap system, but the fact that you don’t smell any fuel would tend to eliminate that possibility.
Another strong possibility is that the evap system’s purge valve is no longer functioning properly.

Or, the carbon canister could indeed be the cause of the problem–especially if you are in the habit of “topping off” the gas tank, rather than stopping as soon as the pump clicks off for the first time. Do you “top off” your gas tank?

From afar, it isn’t really possible to narrow it down any further, so you may need a better diagnostician who can assess the car in person. I would be concerned about paying for the replacement of that very expensive carbon canister if the problem is only the solenoid on the purge valve or a damaged gasket on the gas cap.


Agree with vdc, we even had one car the pump that pressurized the evap system for the test failed, proper diagnosis for a proper repair and less wasted money on unneeded parts and labor.

Oh god. Sadly, I do “top off” to get the nearest “5” or a “0” as the last digit on my total – for absolutely no good reason. Now I feel like an idiot. No one asked me about that habit before, certainly not my mechanic. I will look at the gasket on that cap. Finding a new, decent mechanic sounds like a real challenge… This car never needed any work and the one I’ve got now is the top-rated guy on Yelp. :slight_smile:


There is a possibility that if you stop “topping off,” the canister will dry out in a few weeks.


Thanks. I need to fill up anyway, promise I won’t do anything after the pump shuts off. Still feel like a moron though.

I’m really not trying to “rub it in”, but I have to ask…
Didn’t it occur to you that there was a valid reason for the vehicle manufacturer to put a “Do Not Top-Off” warning on the gas cap, and for most gas stations to have a similar advisory posted on their pumps?


For the life of me, I’ve never seen anything like that on my gas cap, or at the gas stations. This is not at all to find an excuse. Even if you are not trying to rub it in, you absolutely should. Being able to take fair critique is key to being a rational human being and not a donkey. Which I seem to be in this case 100%, especially given my PhD in physics. Ridiculous. So, no worries – bash away.

Another question for everyone. If worst comes to worst with a new mechanic (I was suggested a few options by the locals) and it is indeed the charcoal canister. My current mechanic, usually a chill dude, was very stern about not installing something I’d get on Amazon (priced less than half of his estimate) for a variety of reasons. I can see his point, but want to double check here. Also, are there any decent alternatives to the original Toyota part (which is indeed priced around $400)?

One other thought about ‘topping off’… I refill once a month, possibly even less frequently (very short commute here). Does this make any difference?

The reason the mechanic does not want to install an Amazon or Ebay part is that he will not warranty it and if it is defective neither you or him will be happy. Just let the mechanic source the part so he has recourse and you have a warranty period. As someone else suggested you might wait a while and see if canister clears itself.

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Well, that interval should give the canister some time to “dry out”, but that process will take longer if your neck of the woods is subject to low temps at this time of year.
But, interval aside, repeated episodes of topping-off will take their toll, regardless of how infrequent they are.

If it makes you feel any better, my SO always poo-pooed my warnings about topping-off her Toyota Highlander. “You’re such an alarmist!”, I was told.
Then, when presented with a bill for–IIRC–over $500 by the Toyota dealership, her complaint suddenly became, “Why didn’t you warn me that topping-off wasn’t a good idea?”


The bottom line–IMHO–is that if you are about to cross the Atacama Desert, topping-off your gas tank is probably a good idea. On the other hand, for those us who live no more than a few miles from a gas station, “topping-off” is not really a cost-effective procedure.

Feel free to bring parts to your mechanic, but don’t expect him to provide any type of warranty if they prove to be defective. And, in fact, many mechanics will not allow you to carry-in your own parts for this very reason.

Thanks a lot guys. Lesson most certainly learned.

You’re not a moron.

The EVAP system has a component called a vent/rollover valve.

This valve allows the gas tank to vent while it’s being filled, prevents gas from leaking out the gas tank in the event of a rollover, and it also prevents the gas tank from being overfilled.


Obviously, I never top off to the point of overfilling anything. What I do is a very (and I mean very) short nudge on the pump lever (after the pump shuts down automatically) so that the total ends with a 5 or a 0. Some of my colleagues specialized in efficient combustion systems at Princeton and they agree that forced topping off is not a good idea. Everyone is kind of laughing at me right now. :slight_smile:

Most people pay at the pump with a credit card so the final amount should not matter.

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I am one of them. I honestly don’t know why I’ve been doing that.

5 cents worth is only about 3 US fluid oz (if I did the US units correctly) and I doubt that that amount could cause problems, but I’ll let the experts comment.

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I don’t think rounding up to the nearest 5 cents would hurt the evap system. The canister is 11 years old, it probably has just given up the ghost as a symptom of old age. Evap systems have become very complex, and you really need someone working on this who has evap diagnostic experience and doesn’t take the replace this, replace that approach. Evap canisters can often be removed and bench tested, so ask about that. Better to keep the evap canister you have, particularly if it isn’t broken. Another poster above mentioned the purge valve. That could be the problem here itself, or sometimes when the canister gets saturated in gasoline (b/c of overfilling or it just failed) particles of carbon can lodge in the purge valve, and the purge valve gets taken out with the canister, and has to be replaced. Whatever’s causing the evap codes can be fixed, not a big deal, but it may take a bit of diagnostic time to figure out exactly what’s wrong. Replacing the gas cap might make sense as a first attempt, since that’s cheap.

That swhooshing sound is a little concerning. Unlikely to be related to the evap system. It may just be the fuel pump. But first off, make sure your coolant passes a freezing test. Shops have a gauge to make sure the coolant is good to -20 deg F or however cold it gets there. If icy-slush forms in the coolant overnight, which it shouldn’t if the coolant is strong enough, that can cause a swooshing sound coming from the water pump. If so, that is an immediate problem. Another thing that can cause a swhooshing sound is a defective power brake booster, so ask you shop to check for that while you get the evap problem addressed. Best of luck.

+1 for @BillRussell. A nickle worth of gas shouldn’t cause a problem. Topping off is when you try to squeeze as much as you can in. Sometimes this can be a dollar or more.

I’d start first with the possibility the gas cap isn’t sealing properly, a very common problem and a cheap and simple fix.

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Oh. Then I misunderstood “topping off.” I thought it was something much less substantial.
Then no, I have never done anything even remotely close to what you described.