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2009 matrix gas cap area problem

check engine light came on. Had the code checked and its the code that comes on whhen you dont tighten your cap. Checked fuel cap and the person who was helping noticed that the little spring loaded door that is usually pushed open by the fuel nozzle is gone. So my question is three fold:

  1. will this door that is now in my gas tank hurt my car?
  2. will this lack of door keep tripping this error code? i live in the Milwaukee area where they check emissions so i cant have that
  3. how much is this going to be to fix? I am guessing they can just replace the door or the top part of the fueling system where I put the nozzle in.

This is so embarrassing for me as i work for a Major tool maker in the area and i know squat about this!

Does that car still have a conventional gas cap or is that integrated as well?

I would say its a regular one. The person at the auto parts store said i could buy one for $9

Get it from the dealer and get one there. It is a little more but worth the peace of mind that you have the right one.
Gas caps do go bad and replacing it to see if it fixes it is a cheap thing to try.

That door could be the cause too, though. It could be some integral part of the evaporation system but - for now - let’s hope it is just a door so crap can’t fall in.
I would try the gas cap and see if that light goes back off to get it through emissions.

Edit: here’s a link to a drawing of your fuel tank and related components.
What part fell in, would you say?

I cant tell, I am so not good a figuring out this drawing. I remember it. open the cap there there was a cover that would be pushed open by the gas nozzle when I put it in.

Looking at the components list in RemcoW’s post, a replacement cap and gasket for less than $20 is the way to go. Without the flap gate, you have a big evap leak, causing the code.

I noticed that many cars are using the flap gate caps. I wonder why, and personally just prefer to keep it simple.

PS - I just thought, is this the flap under the cap? For a car this young, you may have other issues with the filler neck, like rust holes to worry about. If a new cap doesn’t turn the CEL off in a couple of days, you meed to have the tank and evap system checked for leaks.

Ok I want to make sure I understand. The gas cap i have is the old traditional type. You unscrew it and it hangs on its cord while you fill up. Once you remove the cap there used to be a little door that would be pushed open by the nozzle and this disappeared into the tank. So if I replace the gas cap this should take care of my check engine code? The little flap door being gone wont cause an issue?

Are you sure the little flap was in there in the first place?

This used to be a very common item in the fill tube of the gas tank but I don’t believe my last few cars have had it.

Back in the 70’s it was common in my neck of the woods that people would punch the “adapter” into the tank as it limited the size of the fuel pump nozzle that could be used on the car, as we all know the fuel pump nozzle for regular (leaded) has is larger than that for unleaded gas. By punching this adapter out of there people could fill up with leaded gas regardless of what it might do to a catalytic converter (if installed).

When we went to emission testing in Lake County Indiana that little flat that you are talking about (I believe) was considered a required part of the emission system and your car would fail if it was not in the fill tube. We sold a replacement flat that would press into the fill tube.

I know my 2000 Miata did not have the flap, I’m pretty sure that my wife’s 2004 Matrix does not have the flap, my 2000 Honda Insight did not have the flap and my 2012 Fiat does not have the flap.

I don’t think you’re going to have an issue.

The person at the auto parts store thought these should be a flap but who knows. Anyone out there with a 2009 toyota matrix or corrola want to open their gas cap and post a picture of what they see?

Bizbonian is right as to why they are there, but if it has fallen into the tank, it won’t hurt anything or cause the check engine light

There is no code that says your cap is not on tight enough. There is a code that can be caused by a loose gas cap, but other things can also cause that code. The next time you get a check engine light, have the code read and record the actual code, then post it here.

BTW, if you are getting this code right after your fill the tank, you may be overfilling the gas tank. That allows liquid gasoline to get into the vent tubes which are only supposed to see vapors. That will set the check engine light and usually gives a P0440, 441 or 443 and occasionally P0446. Always stop filling on the first click.

The spring loaded door on the filler neck is there to prevent gas from running out of the gas tank if the vehicle lands on it’s roof/side as a result of an accident. The gas cap is made of plastic so an impact in that area can easily crack/shatter the gas cap.

It has nothing to do with the Check Engine light.


The code I got was P0442 Evaporative Emission Control System Leak Detected (Small Leak). The auto store person said this was usually due to the gas cap failing or not being tightened properly. I tightened the cap but the code hasn’t cleared. Should I clear the check engine light (I guess I need to unhook the battery) and it doesnt come back I am fine? Or should I go and get a new gas cap and hope it clears?

The auto store person can clear the code for you with his code reader and that is the best way. Go ahead and get a new cap, it won’t hurt and its not a big investment, but if the code comes back, the leak is elsewhere. It should go off by itself after three complete drive cycles without detecting the error.

Keith, many stores don’t clear codes anymore. Some say store policy, others say liability or state law. They will read, but not clear. But, if it is the cap, the CEL will go off after so many cycles without detecting the problem once the cap is replaced. Usually within a week.

The Tacoma throws that code when the gas cap is not on tight. We can argue that there is no such code as a ‘gas cap loose’ code and you’re right - but a loose cap can throw this code, along with other things.
No sense getting stuck on semantics here, guys. Since yours is on tight and hasn’t cleared, get a new cap and see if that fixes it.
If you brought it to a mechanic for that problem, that’s what he’d do for you and charge you an hours labor. If it still throws the code, you’ve at least saved yourself that much.

BustedKnuckles I have not run into that and I can’t speak for store policy or liability, but I don’t think there is a state law against it, at least not if you perform a repair that you believe will solve the problem. In this case, if the OP bought a new gas cap from the auto parts store, then there should be no liability to them for clearing the code, but that would be up to the store policy.