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roonie 05-15-2010 08:59 AM

Check Engine light is useless
Has anyone had this problem?? My check engine light sometimes will come on... stay on for a few miles (50-60) and then go off (assuming I have a couple of engine on/off cycles in there). It seems to be isolated to warmer months... I believe most states dictate a different fuel mixture in warmer months vs winter months. I do not know if that has anything to do with it. My jeep was doing this last summer and I assumed it was the locking gas cap which was a pain. I replaced the locking gas cap with a standard Jeep cap and I have not had any problems until about a month ago which makes me think it might be the fuel mixture issue.

The jeep does not run any different with the light on vs off and its computer seems to reset itself in some way after a couple of restarts. I am not terribly worried about it... but it is beginning to bug me and it effectively makes the check engine light useless.


Just for completeness... my jeep is 2004 - 6cyl.

burton160w 05-15-2010 09:40 AM

Wait, have you checked the codes yet to see what the CEL is throwing at you?

The first option is to go to AutoZone and have them pull the code

The second is to turn the key from the Off to On position three times (not the start position) in rapid succession. The odometer should change and then spit back some numbers ending in 55 eventually. Give us those numbers and we can interpret the code.

stevens243 05-15-2010 10:57 AM

x2. Pull the codes.

After the CEL goes out, they are still stored on the computer.

Not sure if they have smog checks or vehicle checks in NC but anywhere they check ODBII, the codes will still be there and they won't pass your vehicle.

s3nt3nc3d 05-15-2010 11:15 AM

Sounds to me like the CEL is doing exactly what it's supposed to be...warning you when it detects a problem condition. Can't blame it for your not pulling the codes;)

JDsDream 05-15-2010 01:51 PM

I have a similar problem, but mine only occurs in winter. I pulled the code a long time ago and it was slow response os2 bank 1. It would stay on for a few starts and then go out. Dealer would not deal with it unless is was on and it never lasted long enough to get it there. The code was not cleared and the Jeep passed emissions. You just need to pull the code and then check here.

click here > Most Complete List For Jeep Check Engine Light Codes

TJeepman 05-15-2010 02:29 PM

My guesss would be EGR valve, O2 sensor or evaporative control system. Since it's seasonal, probably the evaporative control system. Your changing the gas cap and having no problems for a long time afterwards, seems to support that as well.

Do the "key dance" and see if you get a P0456 code. I recently got the CEL and when I checked the codes, it was P0456. I took the negative battery connection off for a while, while I was doing something else, reinstalled and the CEL/code hasn't retuned.

NjTJ 05-15-2010 02:57 PM

Does the key turn trick work on OBD II vehicles like my 98?

rrich 05-15-2010 03:50 PM

The CEL is useless, but no more useless than the guy that doesn't bother to check what it's telling him.

It will not send you a text message, YOU have to pull the codes from it.

When the CEL first turns on it means the computer is detecting something that's not quite right. If for some reason the fault is intermittant or goes away - either permanently or temporarily, the light goes out again.
All it's saying is something is wrong somewhere.

But - the computer remembers why the light came on - if you pull the codes it will tell you why even if the light is out again!

Most faults will store the code. But you have to find out the code and look it up - it will not fix itself!

Sorry, Magic won't be available till 2012.

bluedragon436 05-15-2010 04:03 PM

Why can't Jeep come with Onstar... maybe then it could shoot you a text with the issue... I have had the same thing on my 98' XJ in the last month on semi warm days... but it goes away, and when I do take it to the zone to get the codes checked there is nothing to read... and the guy looks at me like I am a retard for wanting to check my codes since the light isn't on... I almost punched the dude for getting smart with me the other day, and took his damn reader so when it came on again I could plug it in and check it right then and there...

TJeepman 05-15-2010 05:11 PM


Originally Posted by NjTJ (Post 625012)
Does the key turn trick work on OBD II vehicles like my 98?

If you have a digital odometer, yes. From this site:

OBD-II information is more complex, so the codes for 1998 and newer Jeeps can't be displayed by flashing the check engine light. However, those vehicles which have digital odometers will display the codes on the odometer. I've verified this personally on a 1999 WJ. For those vehicles without digital odometers, or for anybody who wants an English description rather than just a numeric code, an OBD-II code scanner ($100-300) can be plugged in under the dash. OBD-II codes can be looked up online here.

burton160w 05-15-2010 05:53 PM


Does the key turn trick work on OBD II vehicles like my 98?
Actually, you can't. The key-dance trick for some reason was taken away on the 1998 model (late-1997 & early-1999 too). The only way to find out if it will work is to check, but mine (early-1999) hasn't worked :rolleyes:

roonie 05-18-2010 07:37 AM

Thanks all... I will try the key thing. Like bluedragon said... I took it to autozone, they checked the codes... of course by then the light was out and they gave me similar looks as blue.

That is what is perplexing... I don't really have anything to tell my mechanic or the dealership. The jeep is running fine... no troubles at all... knock on wood.

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