Gas cap / Fuel Filler Cap Issue

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LexustoMazda

Member
:
2008 Mazda CX-9 GT Awd
Hello guys,

When i driving my cx-9 today, suddenly the fuel filler cap warning lights turn on. I turn off the engine, check the cap, it seems fine, then i started the engine again, but the warning lights stays on. I've been doing this process for about 2-3 times, yet no effect. The last time i fill it with gas was last week.

Any kind of dangerous issue that i probably had? I'm planning to do a roadtrip next Thursday for about 200 miles, is it safe to drive my car under current condition with fuel filler cap lights on?

Hope to see your reply and Thanks!!!
 
I've been experiencing this same problem with my '10 with about 19000 miles. For the past 3 months it has been an off and on again problem. I finally started making notes, and discovered that when the tank emptied half way the light would come on. This happened 3-4 times consistently. I called my dealer service writer - who needed to check a bulletin and call me back (that was about 10 days ago). [Legend Mazda, San Antonio]. I believe what is happening is the cap isn't venting properly, and is creating a suction sufficient to upset the sensor. This tank full, I watched it closely and when it got down to about half, I released the cap, and put it back on. Now as I go through the remainder of this tank, I'll be watching to see the result. If I do not get a light, I'm sure I'll need a new cap. It should be covered under warranty as a part of the emission control system, and seems like that's 5/50,000. Some of the members here can probably answer that without going to the manual.

I would think a 2008 is right on the verge, depending on the mileage of the vehicle, and date of original delivery. I believe a good dealer is going to take care of that.

One other thing, the manual does indicate that if the cap isn't on correctly, once it's corrected, it will take multiple driving cycles to allow the system to reset. You can read about driving cycles in connection with this symptom in your manual. I wish us both good luck!!
 
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drchuck, when the light turn on, my fuel tank is approximately below half tank. My cx-9 got about 58k miles, so i guess i'm out of luck regarding the warranty :(

Noob question, is it possible that the gas will evaporate if the gas cap aren't correctly put back on (because the gas cap lights turn on)?
 
I might be wrong, but Washington state, like CA, has emission warranty of 7yr/70K miles.
 
Loose cap wont let gas evaporate, unless its an extreme case, but a new cap should fix that, air fuel mixure will be screwed up trigerring emission sensors
 
gas isn't going to evaporate. you can probably get a new cap at any auto parts store, doesn't have to be the dealer.
 
As a followup, I am well below half tank tonight (like 40 miles to empty) and no sign of a light. In fact, when I start the engine, it is the first light to go out. It does sound like LexustoMazda has the same symptom. I think He can check it the same way I did - fill up, allow the driving cycles to extinguish the warning light, and see if it repeats at the half tank area. Irrespective of the cost, it would be far better to pay for a new cap than take a chance on running a lean mixture. (assuming the cap would cause the sensors to read too much fuel, and lean the mixture out). At any rate, everyone on the planet has to breathe this same air - so . . .
 
Sorry, I missed the second question: Yes, I believe the fuel can evaporate at a faster rate of the cap is not securely in place.

As overkill to the answer: I found (if you look inside the gas cap) one can see a series of vent holes around the cap. They are going to direct the evaporating fumes back into the tank which is going to send a value to the EVAP canister, and if the values are not within the parameters the computer is expecting then it's going to signal trouble. In this case the question mark is what could cause that value to change - a leak in the tank, or improper values from the cap.
 
Fuel filler caps do wear out, just like radiator caps. If this is covered under the 7yr/70k mi powertrain warr, then take it to the dealer and let them diagnose. Otherwise, replacing a fuel cap is cheap and you can always try that as the first fix. You can get new fuel caps at any auto store or of course at the stealership. Just have to call around. The online stores might be cheaper depending on shipping.
 
Thanks for your reply guys. I just fill up my gas today, and guess what... The gas cap lights turn off :)

As dr chuck said, i will monitor my fuel gauge whether if it below half tank, the warning lights will turn on again or not.

One last thing, is there a DIY guide on replacing the gas cap? I have search this forum, yet i can't find any.
 
LexusToMazda,
Just to make sure, did you tighten the cap enough (after 2 to 3 clicks)?
 
^ceric

Yes i did, if i didn't tighten it, then the warning light will turn on. I just fill up the gas and the problem hasn't showed up yet.
 
That's a good question, Ceric, I generally spin mine about a half dozen, or so, clicks. The way the caps are designed it seems there isn't any way one could put too much force on getting the cap too tight.
 
As a follow up for this issue, the problem never happen again to my cx-9. I don't know if there is a glitch in the fuel cap sensor or else, but it seems weird if that only happen once and never happen again until now.
 
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