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Check Engine Light

132K views 33 replies 15 participants last post by  JeepCares 
#1 ·
I just got my car 2 weeks ago...and the check engine light came on this morning. I checked the gas cap and it was tight...what else could it be???
 
#2 ·
More then likely it is the gas cap (especially if you recently had a huge temperature swing, like we did here in Philly this past week). Take it off, wipe the filler neck rim and the cap O-ring off (there could be some dust/dirt not letting it seal properly) with a damp paper towel, and put it back on a few clicks. It may take several start/stops of the engine before it resets the light though (5 key on/off cycles sticks in my head). If it does not go out though, try Advance Auto or AutoZone, they read codes for free (if the jeeps not under warranty) then post the code back here so we can help. Good luck!
 
#6 ·
I got a check engine light this spring. The gas cap was OK. My scan gauge said that it had a code which came out to "problem with the temperature sensing system". I had used my engine block heater on a morning which wasn't that cold. I think that when I started the engine the computer saw the engine as being significantly warmer than the intake air temp after sitting for more than eight hours and said "Wrong". After three or four cycles of having it shut down for more than eight hours, the light went away.
 
#7 ·
My GASCAP came on yesturday.. I had a very empty tank and put 20 liters in.. Been there.. Today I went and filled up on gas and turned on the ignirion, GASCAP came on and dissapeared a second later!!! Hehe!!!

But check engine came on today in the afternoon while the GASCAP light was still on. I think it happened after I slammed the brakes as the dude infront slammed his... That's when I notice the check engine light come on.

Though even though the gas light is off the engine light still remains ;(

Called Jeep and they told me as long as car drives then its fine and if still on after the weekend than to come in.

Parts source offer free code reading, but do you think they can mess things up? I may go to them tommorow.
 
#12 ·
With OBDII cars, the light can turn itself off if it no longer detects the fault for a certain amount of key on-off cycles. So if the cap is loose, the light won't go off right away once you tighten it back on. It may be 5 to 10 trips later.
 
#11 ·
cinnepa, it could be you just need to change the spark plugs. Patriots use standard copper plugs, no long life platinum's here. They should be changed every 30k miles, so you are right near the limit. Make sure who ever changes them uses die-electric grease in the rubber spark plug boots liberally.
 
#13 ·
back to dealer tomorrow, they changed plugs last thursday....friday around lunchtime, light came back on after a quirky shift i made. turned jeep on, pulled out of parking space in drive, drove a hundred feet maybe....stopped, put in reverse to let someone else out then right back in drive (the reverse then back to drive took about 10 seconds).....just after this the engine light came back on, and has not gone off since. took to autozone again; same analysis - "cylinder 1 misfire". jeep runs fine, could it be maybe something electrical??
 
#14 ·
It could be the rubber boot on the coil. If they don't seal properly to the plug they can actually fire the spark sideways into the spark plug tube that everything sits into the head on. Die-electric grease helps seal the boot and give a high resistance path. Once they start arcing like that they tend to leave carbon tracks on the boots and the ceramic insulator of the plug (little black lines) and each time it gets easier for the arc. Or the coil itself could be going bad. If you can switch #1 coil with #4 (two outermost coils), give that a try and see if the code changes to #4 misfire.
 
#17 ·
Well, you've eliminated a bad coil and/or coil boot as the problem. Now the problem is definitely in the #1 cylinder so spark plug, fuel injector (could be dirty or clogged in some way causing a lean misfire, or leaking fuel causing a too rich misfire - look at the spark plug to determine), electrical wiring for the coil or injector, or at the worse, a mechanical problem with that cylinder (burnt exhaust valve, or head gasket problem). Again, switching the spark plugs or fuel injectors between cylinders can eliminate those as culprits. A compression check (or better a leak down test) can check the mechanics.

Let the dealer know you've already switched the coils and got the same result.
 
#19 ·
shop switched #1 and #2 fuel injectors yesterday to see if it may help.....message they were getting said something about internal/external temp at startup was a few degrees off....making the engine light go on with 10 seconds of startup. they said because it was sitting around for 4-5 months before they sold it, that might have something to do with it. also mentioned good chance the o2 sensor may be off or the computer and timing may need to be reset......if light comes again they told me to take to a jeep dealer, where they would pay whatever cost the jeep dealer would charge to fix it.
 
#20 ·
Good to hear. At least they're trying to fix it. The temp difference could indicate a problem with either the Engine Coolant Temp Sensor or the Intake Air Temp sensor. As for the ignition timing being off, there's nothing going on there. The engines have fixed cam and crank angle sensors and the ignition timing is set and controlled by the computer.
 
#22 ·
a couple days so far and the light has not reappeared with the new fuel injector - hopefully solved. they mentioned potential reason may have been the amount of time the vehicle has been sitting........they purchased it jan 2011, and did not sell to me until a few weeks ago.
 
#23 ·
Engine Light

Just bought our 2008 Patriot about 3 weeks ago - 89000 K. Engine light came on on Monday and hasn't gone off since. Will try the gas cap thing, but we don't get a gas cap message. From what I have been reading - it must be a MS computer - reboot it enough times and it should go away :).
 
#24 ·
Spirit, try getting the code pulled if you can. Most autoparts stores can do this for free. Re-seating the gas cap is usually the best thing to try first, but it may take a few key on-run-off cycles to turn the light off. You might also want to wipe the filler neck off and the O-ring inside the threaded portion of the cap to insure a good seal.
 
#27 ·
Engine Light



Thanks, Hubby tightened the gas cap, even though he said it wasn't loose and it finally went off yesterday (about 1.5 weeks after it first came on). Has anyone ever used one of those code reader devices that you can purchase? I live in Canada and I don't know if/which auto stores may read them for free.
 
#26 ·
....at seemingly random times, most noticeably at changes of seasons and weather. Gas cap, bad gas, excessive temp changes, all seem to trigger it. As long as it doesn't blink at me I tune it out.


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