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Brand new O2 sensor still throwing codes

slick_rick

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Dec 1, 2021
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So today guys after finishing my motor mount....I got CEL codes 12,21, and 55....keep in mind my TJ is a 97......code 21 is for the 02 sensor...I have replaced the 02 sensor with an AC/Delco one from rockauto.....it's brand new....yet I get the upstream 02 sensor code 21 again.....should I buy dielectric grease and ensure the connection?....I have checked connections and this sensor is brand spanking new....what gives?
 

TJ4Jim

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So today guys after finishing my motor mount....I got CEL codes 12,21, and 55....keep in mind my TJ is a 97......code 21 is for the 02 sensor...I have replaced the 02 sensor with an AC/Delco one from rockauto.....it's brand new....yet I get the upstream 02 sensor code 21 again.....should I buy dielectric grease and ensure the connection?....I have checked connections and this sensor is brand spanking new....what gives?

It's because our Jeeps are cursed with the need for Mopar or NTK O2 sensors, just about any other brand will lead to issues.
 
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Jerry Bransford

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NTK, NGK, and Mopar are the only known good brands of O2 sensors for our Jeeps. NTK makes all of those. Bosch is an especially known problem causing brand of O2 sensor, and likely most store brands too.
 
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slick_rick

slick_rick

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So turns out code 12 for the obd1-inbetween OBD2....actually includes both sensors....checked my downstream sensor and it had been loosened up during my motor mount jostling....I first cleaned it with electrical connector cleaner and had to use a zip tie to keep it tight since the damn locking tab broke....cleared ecu...and now no code is showing....problem fixed....
 

Chris

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So turns out code 12 for the obd1-inbetween OBD2....actually includes both sensors....checked my downstream sensor and it had been loosened up during my motor mount jostling....I first cleaned it with electrical connector cleaner and had to use a zip tie to keep it tight since the damn locking tab broke....cleared ecu...and now no code is showing....problem fixed....

Glad you fixed it, at least temporarily. Now just wait until those AC Delco sensors start acting up ;)
 
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Jerry Bransford

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Keep in mind, a sensor code doesn't always mean that it is bad.
It could be telling you the sensor is not seeing what it's supposed to.
X2 my intermittent O2 codes were caused by a bad pre-catalytic converter. Blaine replaced all 3 of my cats and reinstalled my original O2 sensors. No more O2 codes in the 10+ years since that was done.
 

HandOverFist

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Jul 26, 2022
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Any time you fix a problem, it takes several drive cycles to clear the code and shut off the CEL. Unless you disconnect the battery for 30 seconds or so.

Even disconnecting the battery only works temporarily...there is more to it. I even had another computer which made no difference. I'm of the mind that it was throwing codes for no reason at all other than we are dealing with junk to begin with, but that is for another discussion.
 

C.J. Roberts

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Even disconnecting the battery only works temporarily...there is more to it. I even had another computer which made no difference. I'm of the mind that it was throwing codes for no reason at all other than we are dealing with junk to begin with, but that is for another discussion.

If the problem is fixed, it won't throw any more codes. If it does, there is more to do.
 

Jerry Bransford

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I don't think you understand my meaning. The codes were being thrown for no reason other than to have one chase a problem that does not exist.
Huh??? Codes are never generated for a non-existent problem. They may not accurately point at the actual bad component but there is always something wrong that causes a code to be generated.
 

HandOverFist

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It's actually pretty simple...we are dealing with junk electronics and have been for many years. It is also not just a "Jeep" thing either...one of the reasons for me getting shed of the Corvette.

I understand how things are designed to work, but often in the real world that isn't the case.
 
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Jerry Bransford

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It's actually pretty simple...we are dealing with junk electronics and have been for many years. It is also not just a "Jeep" thing either...one of the reasons for me getting shed of the Corvette.
Again, the PCM will NOT generate any DTC codes unless it actually detects something outside of what it's programmed to accept as normal. If a DTC (diagnostic trouble code) is generated there is SOMETHING wrong SOMEWHERE, even though the code may not be pointing and the correct part causing the problem.
 

HandOverFist

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Ever consider the PCM design itself might be part of the problem? I have dealt with computers for many years and you might be surprised just how little things will bring the big things to it's knees. Never consider electronics to be infallible...I've never met such a system.

All of these so called "modern" electronics were slaved onto relatively ancient technology for "perceived" problems. In use there really were no problems as they were working as intended and still do. We have mandated and self inflicted problems...for little gain many times.
 
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