# Check Engine Light - I think it's just a gas cap. **URL:** \ **Category:** In My Humble Opinion\ **Created:** [October 28, 2009, 3:16pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448 "2009-10-28T15:16:55Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Bearflag70](https://avatars.discourse-cdn.com/v4/letter/b/8e7dd6/32.png) [@Bearflag70](https://boards.straightdope.com/u/Bearflag70)\ **Post date:** [October 28, 2009, 3:16pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/1 "2009-10-28T15:16:55Z")
2002 Mazda Protege - Sacramento, CA - 53,000 miles Check engine light came on last week sometime. I have had no time to take it in, but I haven’t driven too much since then. I did have time to go to AutoZone last week but found out they don’t do free code checks in California anymore. I got the oil changed yesterday at Jiffy Lube. They wanted $20 just to pull the code. I said no thanks because they were not in a position to really fix anything if it was something serious. I twisted the gas cap lightly and it seemed loose, so I tightened it. The car seems to be running fine otherwise, but tightening the gas cap does not reset the check engine light from what I was told. I don’t want to spend $20 to $100 having someone read a damn code just to discover the gas cap was loose and I fixed the problem by tightening it up. I’d like to pull the code to see if the code is consistent with a loose gas cap and/or just reset the light to see if the problem was just a loose gas cap or if the light comes back on having tightened the cap. Maybe going back and paying Jiffy Lube $20 isn’t so bad… or should I just reset the light myself? I don’t know cars, but I hear it’s as simple as disconnecting the battery for a minute. I hate the thought of there being a $20+ penalty for failing to tighten a gas cap properly. Thoughts? ---
**Author:** ![JFLuvly](https://avatars.discourse-cdn.com/v4/letter/j/ac91a4/32.png) [@JFLuvly](https://boards.straightdope.com/u/JFLuvly)\ **Post date:** [October 28, 2009, 3:22pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/2 "2009-10-28T15:22:46Z")
Disconnecting the battery can work, if you have solved the problem, but if it’s something else, it’s going to come back on. Twenty bucks is not a bad price to get the codes pulled, as it couold easily be a hundred other things. P.S. I just resurrected and old thread of yours about your friends wife. I am curious as to how things turned out? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [October 28, 2009, 3:24pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/3 "2009-10-28T15:24:04Z")
When did you tighten the gas cap? Some CEL codes take a certain amount of start cycles or miles before they reset (if the problem was corrected). ---
**Author:** ![Bearflag70](https://avatars.discourse-cdn.com/v4/letter/b/8e7dd6/32.png) [@Bearflag70](https://boards.straightdope.com/u/Bearflag70)\ **Post date:** [October 28, 2009, 3:26pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/4 "2009-10-28T15:26:09Z")
> [@Joey\_P](#): > > When did you tighten the gas cap? Some CEL codes take a certain amount of start cycles or miles before they reset (if the problem was corrected). Yesterday afternoon. I still have half a tank of gas left. I have started the car 5x since tightening the cap. I can go some weeks starting my car maybe only 4 times. ---
**Author:** ![Stuffy](https://avatars.discourse-cdn.com/v4/letter/s/f17d59/32.png) [@Stuffy](https://boards.straightdope.com/u/Stuffy)\ **Post date:** [October 28, 2009, 3:27pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/5 "2009-10-28T15:27:27Z")
In every car I’ve ever driven that does this, tightening the gas cap immediately extinguishes the check engine light. AAMCO at least south of you in Stockton is doing free code checks. ---
**Author:** ![muldoonthief](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muldoonthief/32/3188_2.png) [@muldoonthief](https://boards.straightdope.com/u/muldoonthief)\ **Post date:** [October 28, 2009, 3:35pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/6 "2009-10-28T15:35:04Z")
> [@Stuffy](#): > > In every car I’ve ever driven that does this, tightening the gas cap immediately extinguishes the check engine light. AAMCO at least south of you in Stockton is doing free code checks. I’ve seen exactly the opposite - my 01 Caravan wouldn’t reset the light for a day or two after tightening the cap. So I’d wait a few days before shelling out $20. ---
**Author:** ![control-z](https://avatars.discourse-cdn.com/v4/letter/c/eada6e/32.png) [@control-z](https://boards.straightdope.com/u/control-z)\ **Post date:** [October 28, 2009, 3:40pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/7 "2009-10-28T15:40:57Z")
I’d go with disconnecting the battery for 30 seconds or so. The light may or may not go away on it’s own. Honestly if the car is running well and still getting the same miles per tank, a check engine light isn’t the end of the world. I had a car that loved to keep the check engine light on, was still on when I sold it with 180,000+ miles. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [October 28, 2009, 3:54pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/8 "2009-10-28T15:54:37Z")
> [@Stuffy](#): > > In every car I’ve ever driven that does this, tightening the gas cap immediately extinguishes the check engine light. AAMCO at least south of you in Stockton is doing free code checks. It didn’t in my 97 Grand Am. ---
**Author:** ![Bearflag70](https://avatars.discourse-cdn.com/v4/letter/b/8e7dd6/32.png) [@Bearflag70](https://boards.straightdope.com/u/Bearflag70)\ **Post date:** [October 28, 2009, 3:56pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/9 "2009-10-28T15:56:11Z")
So, I disconnect the battery. If the problem still exists, the light comes back on and I read the codes. If the light stays off, then done deal. Right? ---
**Author:** ![control-z](https://avatars.discourse-cdn.com/v4/letter/c/eada6e/32.png) [@control-z](https://boards.straightdope.com/u/control-z)\ **Post date:** [October 28, 2009, 4:04pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/10 "2009-10-28T16:04:44Z")
Yup, no light=no problem, and a light may or may not equal a problem to worry about. It’s usually a loose gas cap or a sensor. Even if you have the codes read, the code may only indicate a symptom of the real problem, it’s just a starting point in the investigation. ---
**Author:** ![Stuffy](https://avatars.discourse-cdn.com/v4/letter/s/f17d59/32.png) [@Stuffy](https://boards.straightdope.com/u/Stuffy)\ **Post date:** [October 28, 2009, 4:05pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/11 "2009-10-28T16:05:28Z")
You know I almost didn’t include that qualifier because I just knew the next several responses would be variants on “well, mine…” :smack: ---
**Author:** ![PatriotGrrrl](https://avatars.discourse-cdn.com/v4/letter/p/9dc877/32.png) [@PatriotGrrrl](https://boards.straightdope.com/u/PatriotGrrrl)\ **Post date:** [October 28, 2009, 4:19pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/12 "2009-10-28T16:19:08Z")
Why pay $20 for one time when you can get code readers for as little as $35? They work on all cars made after 1996. (Of course, the very cheapest readers do nothing but read out the code number and reset it. The better ones give you more information.) ---
**Author:** ![Cowgirl\_Jules](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@Cowgirl\_Jules](https://boards.straightdope.com/u/Cowgirl_Jules)\ **Post date:** [October 28, 2009, 4:20pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/13 "2009-10-28T16:20:01Z")
Did you look in the manual? In my truck, there’s a sequence to turn the key a certain number of times to make it flash the code on the dash. From there, it’s fairly simple to google it. That’s how I found out one of mine was a gas cap too. ---
**Author:** ![Bearflag70](https://avatars.discourse-cdn.com/v4/letter/b/8e7dd6/32.png) [@Bearflag70](https://boards.straightdope.com/u/Bearflag70)\ **Post date:** [October 28, 2009, 4:30pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/14 "2009-10-28T16:30:01Z")
> [@Cowgirl\_Jules](#): > > Did you look in the manual? In my truck, there’s a sequence to turn the key a certain number of times to make it flash the code on the dash. From there, it’s fairly simple to google it. That’s how I found out one of mine was a gas cap too. Yes. The manual only says that there may be a problem with this or that and suggests going to the dealer for service. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [October 28, 2009, 4:49pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/15 "2009-10-28T16:49:46Z")
> [@Bearflag70](#): > > So, I disconnect the battery. If the problem still exists, the light comes back on and I read the codes. If the light stays off, then done deal. Right? Not necessarily. Some problems require the fault to be present under certain driving conditions two separate times before activating the light. If the light stays off for several weeks, then I’d say it’s done deal. ---
**Author:** ![Hozer](https://avatars.discourse-cdn.com/v4/letter/h/5fc32e/32.png) [@Hozer](https://boards.straightdope.com/u/Hozer)\ **Post date:** [October 28, 2009, 5:56pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/16 "2009-10-28T17:56:22Z")
I have a 2001 model and it does this… Its been the gas cap but it usually takes a week or so to clear. Usually when I pull in the shop and they take the car in back to check it - it goes out. They check the code but its nothing. Good thing the guy is my dads hunting buddy 😉 I would give it another few days if its not sounding funky… sometimes it takes the next time I fill up even if I screw the cap on a couple times after the light comes on. Mazda’s seem to be crazy about that gas cap. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [October 28, 2009, 8:35pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/17 "2009-10-28T20:35:14Z")
> [@Cowgirl\_Jules](#): > > Did you look in the manual? In my truck, there’s a sequence to turn the key a certain number of times to make it flash the code on the dash. From there, it’s fairly simple to google it. That’s how I found out one of mine was a gas cap too. Is your truck pre 1995? The only truck I’ve seen that did that didn’t have OBDII. It did have a harness for a reader though. I had to jump to or 4 pins in the harness then turn it on and off like 6 or 7 times and it would spit out the code via the CEL. ---
**Author:** ![Epimetheus](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@Epimetheus](https://boards.straightdope.com/u/Epimetheus)\ **Post date:** [October 28, 2009, 9:10pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/18 "2009-10-28T21:10:58Z")
> [@Joey\_P](#): > > It didn’t in my 97 Grand Am. Huh, I had a Grand Am (older though, probably 94 or 95) that did this. Also my Kia Sophia had this problem. Tightening the gas cap and unhooking the battery didn’t do anything. I ended up paying 60 bucks, because lights on my dash annoy me. My current car (Nissan Versa) has had the stupid “low tire pressure” light on for some time, but it doesn’t say which tire, and I don’t know of any places that offer free air for car tires around here. Also, I don’t have quarters, so if it isn’t free it is a hassle going to the bank to get rolls of quarters (I never carry cash). ---
**Author:** ![Dripping](https://avatars.discourse-cdn.com/v4/letter/d/d2c977/32.png) [@Dripping](https://boards.straightdope.com/u/Dripping)\ **Post date:** [October 28, 2009, 9:25pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/19 "2009-10-28T21:25:19Z")
Several of the big-chain auto parts stores will read your codes for free, just call around, I think Auto Zone does it. ---
**Author:** ![Bearflag70](https://avatars.discourse-cdn.com/v4/letter/b/8e7dd6/32.png) [@Bearflag70](https://boards.straightdope.com/u/Bearflag70)\ **Post date:** [October 28, 2009, 9:29pm UTC](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448/20 "2009-10-28T21:29:12Z")
> [@Bearflag70](#): > > I did have time to go to AutoZone last week but found out they don’t do free code checks in California anymore. > [@Dripping](#): > > Several of the big-chain auto parts stores will read your codes for free, just call around, I think Auto Zone does it. I think CA passed a law. [Next page](https://boards.straightdope.com/t/check-engine-light-i-think-its-just-a-gas-cap/515448.md?page=2)