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Author Topic: Check engine light on, but no error code  (Read 5252 times)

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Offline Danny in Galveston

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Check engine light on, but no error code
« on: January 29, 2012, 07:05:30 PM »
I don't know what is going on.  My check engine light comes on, self check did not show any error codes.  Cleared the light and it came back on two days later, still showing no errors.  Took it to the shop to put it on the scanner and still showing no errors.  He cleared the light and suggested changing the upstream O2 sensor if it came back on again.  It did and I did, cleared the light and three days later the light is back on again.  The  engine starts, idles and runs great and mileage has not been affected.  WTF?!
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Offline Danny in Galveston

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Re: Check engine light on, but no error code
« Reply #1 on: January 29, 2012, 07:21:18 PM »
Sorry forgot to mention, jeep is a 2001 TJ 2.5l with AX5 tranny.  It has just over 100,000 miles on it.
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Offline sharpxmen

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Re: Check engine light on, but no error code
« Reply #2 on: January 29, 2012, 07:40:42 PM »
leave it so it can do the re-learning before you clear/reset the computer again. it needs 50 some cycles to get its bearings, dunno why is not showing codes but i remember reading somewhere that if you reset it  the obd2 will flash the CEL to report that is not ready but no actual codes are stored, i can't confirm if this is accurate or not (the explanation i recall was that is for emissions reporting so you don't reset the computer before inspection, i have no idea if this is true).
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Offline Danny in Galveston

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Re: Check engine light on, but no error code
« Reply #3 on: January 29, 2012, 08:23:39 PM »
Thank you, that makes sense.  I'll give it a few days and see what happens, and report back.
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Offline Bounty Hunter

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Re: Check engine light on, but no error code
« Reply #4 on: January 30, 2012, 02:12:35 PM »
Sharp, I've never heard of that, it's been my experience that it stays reset once it's reset, unless another code is tripped.

Check your fuel cap tightness also in case it's an EVAP error code.  Also consider unplugging the sensors from the throttle body and plugging them back in.
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Offline sharpxmen

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Re: Check engine light on, but no error code
« Reply #5 on: January 30, 2012, 02:36:25 PM »
Quote from: Bounty Hunter on January 30, 2012, 02:12:35 PM
Sharp, I've never heard of that, it's been my experience that it stays reset once it's reset, unless another code is tripped.

Check your fuel cap tightness also in case it's an EVAP error code.  Also consider unplugging the sensors from the throttle body and plugging them back in.

i recall reading this somewhere and the guy had the same issue, CEL with no code - i can't tell if that's accurate was just relaying the info as i recalled it. To me it doesn't make sense but that's the only thing i could relate this to - from what i know if the CEL is on then there should be a code stored until is cleared unless the battery (or power to PCM) was disconnected or drained and was cleared due to that. Don't know if the OBD2 Jeep PCM has a diag mode but i know on my camaro you can force it via the connector to display open/close loop (so the CEL would come on/off  and blink accordingly) and of course there would be no codes, that's about all i can think of.
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
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Offline Bounty Hunter

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Re: Check engine light on, but no error code
« Reply #6 on: January 31, 2012, 03:02:31 PM »
I would recommend discharging the capacitors to ensure they codes are erased thoroughly.

Disconnect all the cables to the battery.
Hold the Pos and Neg cables together, being careful to not touch the battery posts.
Turn the headlights on and back off.
Reconnect the battery.
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Offline Danny in Galveston

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Re: Check engine light on, but no error code
« Reply #7 on: January 31, 2012, 05:12:00 PM »
I shorted the cables together as per insructions on this site and www.jeepz.com and also had the service center reset the computer.  No codes ever came up.  Light came back on two to three days after resetting the computer either way.  I will just be patient and see if it clears itself after enough start/stop cycles.  If anything was wrong, the jeep would not run as good as it does, so I will just see if the light clears itself.
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Offline neale_rs

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Re: Check engine light on, but no error code
« Reply #8 on: January 31, 2012, 05:17:24 PM »
Usually some code always comes up, often it's the battery disconnected code.  If you are getting no code at all, that is strange.  Have you tried checking the codes yourself with the key method?

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Offline sharpxmen

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Re: Check engine light on, but no error code
« Reply #9 on: January 31, 2012, 05:25:19 PM »
i'm wondering if there is some sort of volatile code (or sets of codes) that would only show if the CEL is on when the scanner is connected (like a runtime code vs a code that is stored) - dunno if such thing exists or not.
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
Latest: Corbeau BajaRS heated seats :dance: keeping warm the rear end

Offline Danny in Galveston

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Re: Check engine light on, but no error code
« Reply #10 on: January 31, 2012, 05:32:52 PM »
Yes, I did the self-test as per the FAQ section of this site, and I also had the service center do a diagnosis.  No error codes.  Disconnecting the battery throws a disconnected battery code.  Clearing the memory clears the memory and the light.  Two to three days later the light comes back on, and there are no error codes.  Again, I will go with the suggestion of 50 start/stop cycles to see if the light clears.
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Torch_Ind

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Re: Check engine light on, but no error code
« Reply #11 on: January 31, 2012, 05:36:52 PM »
being it's a 2001. any code triggered should be stored in history with counts. if the light is on when scanned it should have a cel triggered code.  I have seen bad pcm/ecm that could cause that problem.  I would also get a wiring diagram and make sure you don't have cluster or wiring problem. check if the engine light is ground controlled or power controlled.  if you have short or something it could cause just the light to come on but not by the pcm/ecm.  but this is a very weird problem and may just take some time and diag to figure out.  look for mouse or animal nest lol
« Last Edit: January 31, 2012, 05:37:45 PM by Torch_Ind »
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Offline Danny in Galveston

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Re: Check engine light on, but no error code
« Reply #12 on: January 31, 2012, 05:57:01 PM »
I had this same problem a few years ago on my Ford Ranger, had it checked by two different facilities, no codes showing up.  They cleared the light, it came back on a couple weeks later.  I cleared it a few times.  Finally it quit coming on and I never had a problem with it again.  This was also about 100,000 miles on it.  Coincidence??
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Re: Check engine light on, but no error code
« Reply #13 on: February 14, 2012, 07:32:28 PM »
you probably have this cleared up by now but maybe not.  just because a genaric scanner can't find the code doesn't mena it doesn't have a code.   most affordable scan tools do basic emmision diagnostic codes.   so you have a bad O2.. it'll find that code..    you have an EGR that operate improperly..  it'll find that code..   but there are non emmision affecting codes that a basic scanner cannot retrieve.   the jeep dealers computer can search for MANY codes..   so can a scanner such as auto enginuity (this is the scanner i have)  i ran into this with my powerstroke ford.  our mac scanner said everything was fine..   but the auto enginuity scanner picked up a weak #2 injector code, a code for low FICM voltage performance and a couple others..    hell it'll tell ya if the gas guage doesn't read correctly..
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Offline Danny in Galveston

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Re: Check engine light on, but no error code
« Reply #14 on: March 23, 2012, 09:18:19 PM »
Sorry it took so long to provide an update on my CEL problem, I work offshore on an oil rig a month at a time.  Finally brought my Jeep to the dealer and $248.63 later they figured out I had a bad hose to the evaporative fuel emissions canister.  Replaced the lines, cleared the light and three days later and counting the CEL is still not coming back on.  Dealership said even the best hand-held scanners would not show this problem, only the scanner at an authorized Jeep dealership.  Guess they have to make a living too.
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