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Old 07-30-2013, 09:38 AM   #1
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new to the jeep world.. check engine light

This may be in the wrong area.. but my check engine light keeps coming on. I took to o'reillys and they hooked a computer up to it and found that it was the gas cap... but it was tight.. so the o'reilly guy said to get a new gas cap so I did.. and then I cleared the check engine light.. after a day it came back.. its really frustrating.. its a 1999 Jeep Wrangler Sahara

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Old 07-30-2013, 09:43 AM   #2
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Welcome to the forum and the Jeep world. Have you had the code read to see if it is still the same fault?

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Old 07-30-2013, 09:50 AM   #3
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Two things... first, aftermarket gas caps can leak air & cause that same error code so if that is what you bought from O'Reilly's, that might still be your problem. Aftermarket locking gas caps are especially leak-prone. Second, that code can also be caused by cracked/deteriorated rubber fuel lines & rubber fuel system vent hoses. The code is caused by a vacuum pump that applies a vacuum to the fuel system & if any leaks are detected, it generates that CEL.

But first, I'd go to the dealer and get a factory OE replacement gas cap. You can clear the code on your own by disconnecting the battery's negative cable for 2-3 minutes. Or, easier, unplug the ECM's connector closest to the driver's side for 2-3 minutes which does the same thing but without causing your radio to lose its time or radio station settings.
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Old 07-30-2013, 10:07 AM   #4
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Thank you guys for the quick reply.. Awesome stuff guys..
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Old 07-30-2013, 10:08 AM   #5
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could this also affect gas mileage?
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Old 07-30-2013, 10:12 AM   #6
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It should have no effect on gas mileage.
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Old 07-30-2013, 12:57 PM   #7
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I went back to o'reilly and the code from the machine that can check the computer states the code is p0138 code definition is 1 2 O2S SHORTED TO VOLTAGE. is this something easy to do myself ... keep in mind I am not mechanically inclined but I sure want to learn.
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Old 07-30-2013, 01:03 PM   #8
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It sounds like a bad o2 sensor. A very common trouble point on our Jeeps. Make sure that they are replaced with NTK brand sensors only!! rockauto.com is the cheapest place to order them from. Litterally half the cost of what advance auto wants for them. There should be no reason why you can't do this yourself.
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Old 07-30-2013, 02:08 PM   #9
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Welcome to the Jeep world
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Old 07-30-2013, 03:32 PM   #10
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Is this replacement of O2 sensors something I should do or let a mechanic handle it.. I was quoted 160 for both sensors thats parts and labor but it would be next week before he could do it.. its a nurse that I work with her husband
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Old 07-30-2013, 04:38 PM   #11
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Quote:
Originally Posted by Big Sarge View Post
It sounds like a bad o2 sensor. A very common trouble point on our Jeeps. Make sure that they are replaced with NTK brand sensors only!! rockauto.com is the cheapest place to order them from. Litterally half the cost of what advance auto wants for them. There should be no reason why you can't do this yourself.
Thanks for the info about rockauto.com
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Old 07-30-2013, 04:45 PM   #12
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Quote:
Originally Posted by dabeardedjeepguy View Post
Is this replacement of O2 sensors something I should do or let a mechanic handle it.

Can you work a ratchet? I am no master mechanic and I swapped out a bad one in a few minutes. Unplug the connector and unscrew the sensor. You will need to buy/borrow an oxygen sensor socket from the parts store. The only thing I could think of that would hold you back is if the sensors were stuck in place due to rust (shouldn't be a problem in SC, though).


Quote:
Originally Posted by dabeardedjeepguy View Post
I was quoted 160 for both sensors thats parts and labor
If you go this route make sure he uses NTK brand sensors and definitely not Bosch brand sensors.
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Old 07-31-2013, 09:02 AM   #13
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Ok guys it looks like its the upstream sensor from the readout at Advance Auto Parts.. can anyone tell me the part# I need for a 1999 Jeep Wrangler so I can attempt it myself.. Do I need the sensor part (looks like a spark plug) and thats all or do I need more ? Thanks so much
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Old 07-31-2013, 09:12 AM   #14
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This is for the upstream

NTK Part # 23151

Downstream

NTK Part # 23099

They are about $34 each from rockauto.com here is a 5% discount code as well for them


1574541712895315




Using Your Discount Code

Enter the code above in the "How did you hear about us" line of the shopping cart. If you are using our traditional HTML catalog, please click the "Apply" button to the right of the field. Your discount will automatically appear, subtracted from your parts order total. Orders using discount codes must be placed online. Phone orders are not eligible for discounts.

Please note: We sometimes get calls from people who put the word "discount" in front of their code and do not get the discount. Please enter ONLY the discount code, no other words or numbers. Code must be entered before order is submitted to receive discount.
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Old 07-31-2013, 10:58 AM   #15
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Thanks Big Sarge
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Old 08-03-2013, 07:32 PM   #16
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Check your cat. Have someone shake it, make sure it doesn't jiggle inside. There is an O2 sensor above the cat. I had my O2 sensor changed, same problem. The O2 sensor was working properly. After 14 years, the cat may have broken loose internally, from road use. Mine was jiggling madly inside. It's glass inside. Glass breaks easily, especially after 14 years. This is a cash register for the dealership. The dealership rebuilt my heads, changed my tranny fluid, changed my O2 sensor, did all the maintenance. $2000.00 dollars, and a couple days later, the check engine light was back on.

Took my vehicle somewhere else, and they found the problem. The dealership obviously knew, because the O2 sensor was directly above my broken cat. Changed my cat, problem solved. If that cat is bad, your problems are just beginning. Loss of acceleration, stalling, unable to get above 40mph, back fires, uncontrollable high revs, can't get into second gear, etc. Good luck.

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