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Unread 12-17-2013, 07:30 PM   #1
Zyurazek
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Engine Light codes?

Hello, I am new to this forums. I signed up after reading many topics on here for help with my Wrangler. I am new to the world of Jeeps. I purchased my 95 Wrangler SE 4.0L standard shift a few weeks ago. I had my engine light come on. After getting the codes, I was left a little stumped. The codes came in this order: 12 (battery disconnect), 51 (rich mixture I believe), 21,21 (that is no error, 21 registered twice. I am stumped as to why is flashed twice.), then a 55 which is the end of the codes. Is the 51 and 21 due to an O2 sensor? Does anyone have any idea why 21 would flash twice? I would appreciate any thought! I've searched the topic and there was only 1 other post a couple years ago, but there was no solution.

Thank you!

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Unread 12-17-2013, 07:59 PM   #2
Louie4
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Sounds like an O2 sensor based on what you've said. You may always want to check the catalytic converter also. If they start to clog they will heat up the sensor and burn it out.
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Unread 12-17-2013, 08:05 PM   #3
Zyurazek
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The exhaust from the header to the muffler has all been replaced just 3 weeks ago.
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Unread 12-18-2013, 05:46 AM   #4
Mark05059
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check for a leak near the head or header.
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Unread 12-18-2013, 06:51 AM   #5
pete1991YJ
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Welcome to JeepForum, you've just found one of the best jeep sites anywhere!

The other guys are right, it sounds like an O2 sensor problem or possible a header leak. They are known to get loose near the back of the engine, I usually snug up the manifold bolts a couple times a year just to be sure. It only takes a few minutes with a 9/16 wrench.

After you get done you can reset the computer by disconnnecting the battery for a minute. The drive it for a bit and see if the error comes back. If it does then I would consider the O2 sensor.

hope that helps!
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Unread 12-20-2013, 07:25 PM   #6
laybackman
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code 21 21 is code 33 AC issues if you have no AC that is the issue

Any leak in the intake system from a loose throttle body to a crack in the exhaust to a loose O2 sensor will cause a false lean code and make the engine run quite rich.

The O2 sensor detected oxygen in the exhaust stream and sets the DTC.

The O2 sensor is usually the least guilty for the O2 sensor code. A leak allowing atmospheric air into the system is the usual culprit.
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Unread 12-22-2013, 08:14 PM   #7
Zyurazek
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Thanks for all the help! I've checked some things over and I've come up with having a bad sensor. I'll be replacing that sometime tomorrow to see if that's the definite fix!

For the 21-21 code being for the AC, I do have AC in my Jeep, and it seems just fine. I cracked it up today since the weather decided to go anti-winter and climb up to 70 plus degrees. What could it be if physically it feels fine?
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Unread 12-22-2013, 08:48 PM   #8
laybackman
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Quote:
Originally Posted by Zyurazek View Post
Thanks for all the help! I've checked some things over and I've come up with having a bad sensor. I'll be replacing that sometime tomorrow to see if that's the definite fix!

For the 21-21 code being for the AC, I do have AC in my Jeep, and it seems just fine. I cracked it up today since the weather decided to go anti-winter and climb up to 70 plus degrees. What could it be if physically it feels fine?
I WAS WRONG!

DTC 21 = O2 sensor stays at center or shorted to voltage. Neither rich or lean condition detected from the oxygen sensor input.

If the wiring is good then the sensor is probably junk
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Unread 12-22-2013, 08:55 PM   #9
Zyurazek
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Quote:
Originally Posted by laybackman
I WAS WRONG! DTC 21 = O2 sensor stays at center or shorted to voltage. Neither rich or lean condition detected from the oxygen sensor input. If the wiring is good then the sensor is probably junk
Makes more sense! Thank you!
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