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Check engine light and O2 sensors

WWII Jeeper

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Feb 18, 2017
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377
Location
Broomfield, Colorado, United States
I don't know anything about PCM's. The OP said the problem has existed for "several years", so is it possible for the pcm to be stuck in those modes for that long without failing in other areas? Seems that it would show other things if the pcm was defective.

Love this site for all the great ideas. Right now I don't have any of these problems, but at 90+K, some may come, and now I have the possible fixes.

For rmckinney:
Even if you are not a "mechanic", look over the post Chris gave you and think about replacing all the sensors yourself. You might be surprised at what you can do. You would be in your own garage or wherever, on your own time with no deadline (hopefully). The experience you get from that just might come in handy one day if you breakdown on the trails. It's a Jeep....have fun wrenching on it, don't stress, and learn. :)
Ray
 

81laredo4sale

New Member
Joined
May 10, 2018
Messages
1
Location
Ponchatoula, LA, USA
My 2006 LJ had the same issues, checkengine liight on for O2 sensors. Changing the gas cap didn’t work this time (but has before) and disconnecting battery did. No more light. Thanks guys!

(Maroon 81 Laredo, supposedly 1 of 500 automatic, for sale) contact Amy [email protected] for more info
 

gatortad

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Joined
Jul 23, 2018
Messages
4
Location
Indio, CA
I have a similar check engine light problem with the o2 sensors. I replaced the o2 sensors still check engine light. Took to dealership who diagnosed it as a pcm failure. Waited 4 months for a replacement pcm only to have the same o2 codes come up again. Dealership says thereplacwment pcm is bad and has ordered another one. The projected replacement not expected to arrive until Dec. 31!!! Could it be something else besides the pcm? Help, please.
 

Tray

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Joined
Sep 1, 2018
Messages
2
Location
Hampton
I have a similar check engine light problem with the o2 sensors. I replaced the o2 sensors still check engine light. Took to dealership who diagnosed it as a pcm failure. Waited 4 months for a replacement pcm only to have the same o2 codes come up again. Dealership says the replacwment pcm is bad and has ordered another one. The projected replacement not expected to arrive until Dec. 31!!! Could it be something else besides the pcm? Help, please.


I just bought a Jeep Wrangler, and am researching these issues with O2 Sensors and the TJ Jeeps. After reviewing the Service Manual, The PCM has two main power grounds, all the sensors return to the PCM and share these 2 common grounds,The sensor return comes into the sensor return circuit, passes through noise suppression and is then connected to the power ground. I think this could be the key to all the 02 Sensor Issues on the TJs. My best guess would be to ground to different power grounds, but I am not positive if this would even work. I am thinking the noise suppression is likely causing these strange 02 issues. Just my thoughts, doesn't mean I am right.
 
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gatortad

New Member
Joined
Jul 23, 2018
Messages
4
Location
Indio, CA
I just bought a Jeep Wrangler, and am researching these issues with O2 Sensors and the TJ Jeeps. After reviewing the Service Manual, The PCM has two main power grounds, all the sensors return to the PCM and share these 2 common grounds,The sensor return comes into the sensor return circuit, passes through noise suppression and is then connected to the power ground. I think this could be the key to all the 02 Sensor Issues on the TJs. My best guess would be to ground to different power grounds, but I am not positive if this would even work. I am thinking the noise suppression is likely causing these strange 02 issues. Just my thoughts, doesn't mean I am right.
 

Tray

New Member
Joined
Sep 1, 2018
Messages
2
Location
Hampton

Research

Book: Automotive Technology: A systems Approach, 5th edition.
By Jack ErJavec

Page: 772

Basically bad grounds would cause less voltage at load. With reference voltage sensors, the opposite apparently happens causing high voltage at load, and the computer analyzes this bad information, and so the computer decides to throw a code.

In the book is the process to test for voltage drop across the ground wires.

It makes a lot of sense to me.
 

gatortad

New Member
Joined
Jul 23, 2018
Messages
4
Location
Indio, CA
I had to replace the pcm. After replacing, the o2 heater monitor wouldn't complete. Informed the stealership that I found a service bulletin from 2013 to fix the problem. Involved some rewiring. Fixed the problem. Only cost $1800 thru the dealership. What a bargain.
 

Hoss1374

New Member
Joined
Oct 6, 2019
Messages
4
Location
AZ - Arizona
05 tj 4.0. Have all 4 O2 sensors throwing codes. Replaced all sensors with NGK. Fine for about 20 miles then cel. Researched, Pulled cats, appeared good but replaced anyway. Reset and about 20 miles, cel again. I clear it and as soon as I start up....cel. Any ideas????
 

Jerry Bransford

TJ Guru Moderator
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Nov 9, 2015
Messages
25,464
Location
Fleming Island Florida
05 tj 4.0. Have all 4 O2 sensors throwing codes. Replaced all sensors with NGK. Fine for about 20 miles then cel. Researched, Pulled cats, appeared good but replaced anyway. Reset and about 20 miles, cel again. I clear it and as soon as I start up....cel. Any ideas????
Exactly what CEL code(s) are you getting?
 

Hoss1374

New Member
Joined
Oct 6, 2019
Messages
4
Location
AZ - Arizona
I'll check for that and the 105 grounding strap mentioned above. Will update, thanks.
Couldn't find any bad wireing but did find where it had been rewrapped. Eyeballed but didn't mess with grounding strap...looked ok and didnt want multible possibilities. Reset cel which couldn't do yesterday. Believe you are right I just moved a wire. Will see, may have to find someone with better eyes!!! Thanks again.
 

Dyl_Mac_Mil

New Member
Joined
Sep 30, 2020
Messages
4
Location
South Africa
Couldn't find any bad wireing but did find where it had been rewrapped. Eyeballed but didn't mess with grounding strap...looked ok and didnt want multible possibilities. Reset cel which couldn't do yesterday. Believe you are right I just moved a wire. Will see, may have to find someone with better eyes!!! Thanks again.
Have you managed to resolve this in the long term? Was it bad wiring somewhere? I have the same issue and wiring all looks fine...
 

BamBamAF91

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Joined
Aug 27, 2022
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5
Location
Sumter, SC
Wondering if @Abba77 and @Dyl_Mac_Mil ever found the solution to these? I just received my new @Wranglerfix PCM . It resolved all my trans codes but still have the 32, 38, 52, 58 codes. (Mark, I sent you an e-mail this morning)

My scanner says to replace the Oxygen Sensor Relay but according to the service manual the 2005 doesn't have a relay or a fuse and I confirmed in the power distribution Center, (no relay and no fuse).
 
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Wranglerfix

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May 2, 2019
Messages
745
Location
Hollywood, Fl
Wondering if @Abba77 and @Dyl_Mac_Mil ever found the solution to these? I just received my new @Wranglerfix PCM . It resolved all my trans codes but still have the 32, 38, 52, 58 codes. (Mark, I sent you an e-mail this morning)

My scanner says to replace the Oxygen Sensor Relay but according to the service manual the 2005 doesn't have a relay or a fuse and I confirmed in the power distribution Center, (no relay and no fuse).

Double check the connector plugs, making sure the cpa clicks in. If you have some contact cleaner you can spray the female connectors making sure no buildup. I will follow up with your email tomorrow.

Thanks,

Mark
 

skrelnik

TJ Addict
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Joined
Jan 10, 2018
Messages
2,770
Location
CT, United States
Wondering if @Abba77 and @Dyl_Mac_Mil ever found the solution to these? I just received my new @Wranglerfix PCM . It resolved all my trans codes but still have the 32, 38, 52, 58 codes. (Mark, I sent you an e-mail this morning)

My scanner says to replace the Oxygen Sensor Relay but according to the service manual the 2005 doesn't have a relay or a fuse and I confirmed in the power distribution Center, (no relay and no fuse).

How are your cats? That could be the cause of the four O2 sensor codes. Also, any leaks, possibly the two elbows on the valve cover?

@Wranglerfix - is there any way to check the O2 sensor wiring to see if any are clipped? Without taking all wiring harnesses apart, is there a simpler way to read the PCM to see if there are any issues when the PCM speaks to the O2 sensor?
 

BamBamAF91

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Aug 27, 2022
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Sumter, SC
Double check the connector plugs, making sure the cpa clicks in. If you have some contact cleaner you can spray the female connectors making sure no buildup. I will follow up with your email tomorrow.

Thanks,

Mark

Connector (2nd from right) cover appears to be broken and won’t click in
 
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