every fill up "check engine"

for the last few times i've filled up the jeep i fill the tank put the cap on tight and drive it and within hours or the next time i start the jeep the check engine light come on. i shut the jeep off and take the gas cap off and put it back on and drive it and a few hours later the check engine light goes away. the jeep drives fine no skip or miss ever, even with the light on, i just had it completely tuned up last saturday.

I'm thinking it's a bad gas cap, what do you guys think? I am havign a scanner put onit today just in case though

Yes, start with the gas cap. See this one everyday. Get a good aftermarket, or get the one from the dealer.
Good luck

Buy a scanner of your own, they are like $50 now or a better one that will allow you to reset the light. Having one eliminates a lot of stress when that light comes on..

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RichP said:

Buy a scanner of your own, they are like $50 now or a better one that will allow you to reset the light. Having one eliminates a lot of stress when that light comes on..

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X2. It will pay for itself the first time the light comes back on, and you are able to properly turn it off.

Gas caps do go bad, and quite often. Go to Napa or your favorite parts store and get one. Might also be a good idea to go ahead and get a locking one. The locking cap I got from Autozone for mine cost me somewhere around $11 if I remember correctly.

This maybe obvious so I'll apoligize if you already know better, but you don't fill your jeep with it running do you? Good chance you'll set the ck eng light with the cap off and the key in the run position - engine running or not.

You could always bring it to Autozone and have them scan it for ya

On '97 2.5 sport, battery disconnected for about half an hour will extinguish 'check engine' light.....If problem reccures the light will come back on.
Whilst battery is off, do not operate any part of the jeep ! ! ! ! !
I had problem with TPS putting check engine light on and did the above till i had new TPS fitted..

i have an 01 same thing i ha them scan it where i work and it had random codes for some issue w. the tank when it is between 80-50% full which is exactly when it would be on but she runs fine do i dont bother w/ it

zachxj01 said:

i have an 01 same thing i ha them scan it where i work and it had random codes for some issue w. the tank when it is between 80-50% full which is exactly when it would be on but she runs fine do i dont bother w/ it

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The problem with this thinking is that you'll never know if you have a more serious problem until it affects the drivability of your vehicle. You've only got 1 check engine light, let it do it's job. Best just to resolve the issue like it sounds like you're trying to do.

BTW, are you topping off? If you are, don't. It's not all that common, but it can cause issues w/ OBD II vehicles.

not sure if this was resolved, in the past I had the CEL pop on when I would fill it with higher octane fuel. back in the days I thought it was a good idea (get better hiway milege I thought) and the emissions would mess with my O2 sensors causing a CEL. Reg 87 temporarily fixed that, finding this site and learning higher octane does nothing for a stock engine solved it for good.

well, the check engine light turned out to be a o2 sensor code. i got a new gas cap from the delaership and put that on. My mechanic cleared the code and i drove the jeep around 50 miles so far and it's been fine.

my fathers 01 has been throwing evap codes for the past few months. I shut the light for him and its usually back a few days later. Within 24 hours of getting gas too. A new cap from the dealer cost me under $10 and its been code free for the past 150 miles or so.

i'm surprised that nobody brought up the simple fact of making sure the cap is thight. when working at the dealerships, i've seen cars come in daily with CEL after getting gas. what happens is that people put the cap in place in just give it a little flick until it clicks once. but that's not tight enough. in alot of newer vehicles it even says in the owners manual to make sure it clicks at least 3x (or was it 5x???). anyways, whenever i put my gas cap on, i just turn it once around. it only takes an extra flick of the wrist and saves alot of headache.

please dont buy an OBD scanner just to erase codes...

you are removing the symptoms of a prob, not fixing the prob itself.

lost honda pro said:

please dont buy an OBD scanner just to erase codes...

you are removing the symptoms of a prob, not fixing the prob itself.

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Most people buy them to determine the problem, or determine the issue and get an idea as to where to start in solving the problem. Then erase the code once the problem is fixed, and save themselves the money of having to take it to a shop for a "diagnostics check"

Also, it depends on what the light came on for as to what the problem is. Sometimes it just comes on as a fluke. Resetting the light properly and waiting to see when and if it comes back on is a good way to determine if you actually have a problem, or if it was just something odd that happened for no reason.

99XJSPORT06 said:

Most people buy them to determine the problem, or determine the issue and get an idea as to where to start in solving the problem. Then erase the code once the problem is fixed, and save themselves the money of having to take it to a shop for a "diagnostics check"

Also, it depends on what the light came on for as to what the problem is. Sometimes it just comes on as a fluke. Resetting the light properly and waiting to see when and if it comes back on is a good way to determine if you actually have a problem, or if it was just something odd that happened for no reason.

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i completely agree with buying one to find the problem, but there were several posts that implied buying it to "properly turn off the CEL". if you are trying to fix the problem, then by all means, buy one... i just wanted to make it clear that buying one STRICTLY to clear codes is not only fiscally irresponsible, but poor mechanical procedure.

also, just so the newbies know:

a) you can turn off/clear CELs by pulling the ECU fuse
b) multiple auto parts places check CELs for free (and clear em)

lost honda pro said:

i completely agree with buying one to find the problem, but there were several posts that implied buying it to "properly turn off the CEL". if you are trying to fix the problem, then by all means, buy one... i just wanted to make it clear that buying one STRICTLY to clear codes is not only fiscally irresponsible, but poor mechanical procedure.

also, just so the newbies know:

a) you can turn off/clear CELs by pulling the ECU fuse
b) multiple auto parts places check CELs for free (and clear em)

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Agreed. It's just that a lot of people recomend unhooking the battery for 10-20 minutes to "reset" the computer. THIS is poor practice, and sometimes doesn't remove the code from the computer's memory. Buying a scanner will completely clear it, and not mess up your radio presets

im not sure how the ECUs on these OBD2 jeeps are, but the hondas we did would always cycles the problem circuit for 3 (or 5?) drives before it would erase a non-occuring code... it was a pain in the ass, but the ECU fuse fixed it great

radio presets? what are those? are they on my MP3 CDs?

Catch with OBD-II...

Pulling the battery cable to "reset" the code sets another one - but you don't get a CEL for it. However, if you are subject to inspection, seeing that code (without seeing a new battery in place, for instance) will cause you to fail.

Also, OBD-II has two types of codes - a "soft" code indicates a malfunction, but you won't get a CEL with it. It's a non-critical component malfunction (that "Battery Disconnect within the last xx cycles" is a soft code.) You also have "hard" codes - these are considered crtical component failures or malfunctions, and you'll get a CEL for them. Of course, this usually means "critical" as in "increases emissions" - like the EVAP control code you get from a loose fuel cap.

Long story short - get a reader, and use is periodicially (about once a quarter should do.) You can not only see what "hard" codes are when you get a CEL/MIL, but also read "soft" codes that you wouldn't otherwise (but would probably fail you for inspection,) and be able to reset the ECU DTC properly once it's fixed. Most OBD-II readers for the hobbyist are well under $200, and they do tend to pay for themselves in short order.

Note - if you go to Autozone or similar to get codes read, chances are, they'll only be able to explain the "zero" series codes that are set by SAE. For instance, you can get powertrain codes in two broad categories - "P0" codes are set by SAE and standard across the industry. "P1" codes are set by the manufacturer, are therefore non-standard, and aren't something that a "standard" (read: droid-equipped) outfit would be likely to understand. And, the same "P1xxx" code could mean different things, depending upon the make of vehicle.

OBD-II does make more sense than OBD-I (makes sense - OBD-I was devised by CARB and CalEPA, OBD-II by SAE,) but there are still pitfalls you can fall into...