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Old 02-04-2011, 03:56 PM   #1
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Check Engine Light came on this morning.

My check engine light came on this morning on my way to work. I didn't hear anything, or experience any power drop off. I will check my gas gage on the commute home tonight. Me thinks it is an o2 sensor.

I read in here somewhere that you can check the codes by pushing the trip reset, and rocking the key 3 times, (is this true)?

I have a 2001TJ 4.0 with auto.

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Old 02-04-2011, 04:45 PM   #2
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Turn your key to the on position (not start), off, on, off, on wait a few seconds and the code will appear in the odometer window. After all codes are shown it will read "done"
Then go here to check the code meaning.

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Old 02-04-2011, 05:14 PM   #3
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Advance auto parts lets you use there code readers for free.
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Old 02-05-2011, 09:57 AM   #4
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Yep so long as you don't have a '98-'00 TJ, the years this ability was missing, you can check your own codes and there's no need to have your diagnostic codes read by an auto parts store. No need to push the odometer reset button in, simply turn the key on-off-on (but not to Start) three times within five seconds and then leave it in the on position. Wait, give it time as the codes don't appear instantly, it takes several seconds for the diagnostic routine to run.

Check your gas cap too. If it is loose or if it was off when you started your engine, that will cause a Check Engine light. Sometimes a Check Engine light is set by a momentary glitch too. You can reset the light by disconnecting the battery's negative lead for 2-3 minutes. If the CEL comes back on, then it's time to look into the code reported by the diagnostics and figure out its root cause.
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Old 02-07-2011, 08:51 AM   #5
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Thanks everybody. My code read out as an 05-02? I pulled the negative battery terminal for a couple of minutes, and re-attached. The Check Engine light went out.
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Old 02-07-2011, 09:27 AM   #6
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05-02 isn't a valid code. A valid diagnostic code for your 2001 would have been four numbers following a 'P' like P1234.
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Old 02-10-2011, 04:10 PM   #7
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That's what I thought. I have a buddy with an OBDII scanner, and book, I'll borrow it from him. The good news is, the Jeep is running fine, and fuel consumption is about normal for a Jeep, (15-16 MPG All around).
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Old 02-10-2011, 08:56 PM   #8
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You don't need his OBD II scanner to read your codes, you can read your own as described above. Done correctly, any diagnostic codes will display in your odometer. Read post #4 above carefully again, it tells you how to do it correctly.
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Old 02-10-2011, 09:02 PM   #9
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Quote:
Originally Posted by Jerry Bransford
Yep so long as you don't have a '98-'00 TJ, the years this ability was missing, you can check your own codes and there's no need to have your diagnostic codes read by an auto parts store. No need to push the odometer reset button in, simply turn the key on-off-on (but not to Start) three times within five seconds and then leave it in the on position. Wait, give it time as the codes don't appear instantly, it takes several seconds for the diagnostic routine to run.

Check your gas cap too. If it is loose or if it was off when you started your engine, that will cause a Check Engine light. Sometimes a Check Engine light is set by a momentary glitch too. You can reset the light by disconnecting the battery's negative lead for 2-3 minutes. If the CEL comes back on, then it's time to look into the code reported by the diagnostics and figure out its root cause.
.


Very helpful didn't know this was possible

Also the gas cap is a very good chance . I failed emissions with a 5 month old gas cap . Luckily I always bring a new one , changed it and passed . After replacing gas cap it will take about 20 miles for check engine to go off (if it was the problem)
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Old 02-11-2011, 07:13 PM   #10
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hello new to this website i to have same problem engine light but now comes for awhile then oneday light shuts off so next time lights up try the code see what it reads thanks sharing
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Old 02-11-2011, 07:50 PM   #11
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I have found on really cold days my o2 sensor throws a CEL but when the days get warmer it automatically clears out.
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Old 02-05-2013, 10:12 AM   #12
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I had the issue where my check engine light would come on under heavy loads. It ended up being the #4 spark plug. The gap was incorrect so I was getting a misfire on cylinder #4.
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Old 02-05-2013, 02:51 PM   #13
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Also if you have a problem pumping gas and the pump shuts off too quick and you squeeze the handle three or more times to fill the tank rapidly it will also trigger the engine light. I wait a couple seconds and add gas slowly and after the second shut off I hang it up., No problems since.
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Old 05-02-2014, 03:36 PM   #14
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My CEL light came on this morning, I'm at 47,000 miles (2011), I was wondering if it may be the 'its almost time for your 50,000 tune-up'. It's likely I'm wrong...my prior vehicles had it built in where it set off at the manufactures recommended time at different mileage intervals. I shall find out today and try a couple of the trick above.
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Old 05-02-2014, 03:44 PM   #15
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Until he gets the codes describing your past codes makes no sense. And if he is taking to following everyone guess what his problem is he is wasting time, effort, and money.
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Old 05-04-2014, 09:58 PM   #16
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I don't remember what the code number was, but sometimes when I would cold start the engine when it was cold out as well, the exhaust pipe wasn't sealing tight at the manifold. It would set a code that said the O2 sensor signal was slow response. The MIL would turn on.

When the engine warms up the exhaust pipe would seal up and eventually the MIL would turn off after a few starts.

Turns out the exhaust pipe at the manifold wasn't tight enough and allowed for some contraction and expansion which allowed for fresh air to come in and mess up the O2 sensor signal and setting the code and turning on the MIL.

So don't be too quick to change the O2 if the code gets set. Make sure the exhaust is sealed tight at the manifold first.

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