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OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs. |
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Downstream O2 Sensor Help
ownstream O2 Sensor Help!
All, I cannot pass the DEQ emissions test because I cannot seem to keep my O2 sensor working for more than 1 day. I have replaced my O2 sensor, twice now and get the same results. I get a P0138 code. I have a 2000 Jeep Cherokee Classic 4WD, XJ. Initially, after replacing the sensor, everything is running fine, I get a reading of 0.4-0.42 V from the Bank 1 Sensor 2, then all of the sudden it will start reading 1V and then throws the code. It seems like then sensor works for a couple of hours of running then just gets cooked! The last one I used was a Bosch sensor. I don't know what else, the wiring seems fine and I would assume is good because I get a decent reading for a while before it fails. Is it possible my PCM is just bad? I hate to dump a bunch of money into this thing, just want to keep it going for a few more years! ![]() |
#2
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Re: Downstream O2 Sensor Help
The first thing I would look at is the wiring and it's a special twisted pair.
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#3
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Re: Downstream O2 Sensor Help
Yeah, check the harness and make sure it's not rubbed through somewhere.
Any running issues? Do you have any freeze frame data?
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1988 Laredo 2wd Auto, AKA "Grey Ghost", 206K |
#4
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Re: Downstream O2 Sensor Help
Wiring issues are much more common and much more likely than PCM issues.
P0138 JEEP - O2 Sensor 1/2 Circuit High P0138 JEEP Possible Causes •Faulty Rear Heated Oxygen Sensor Bank 1 •Rear Heated Oxygen Sensor Bank 1 harness is open or shorted •Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection •Intake air leaks •Exhaust gas leaks
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. ![]() . Quote:
Last edited by Tim_MN; March 11th, 2020 at 11:18. |
#5
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Downstream O2 Sensor Help
![]() What should I be reading voltage wise from the vehicle across the heater terminals? What about the O2 sensor? Sent from my iPhone using Tapatalk |
#6
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Downstream O2 Sensor Help
This screen shot is from this morning.
![]() Last night it was reading .4 V on o2 bank1 sensor 2 Sent from my iPhone using Tapatalk |
#7
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Re: Downstream O2 Sensor Help
I had almost the exact same issue, I can almost guarantee the wiring got destroyed by the drive shaft. Follow the harness wiring and you'll see the wires got rubbed out and is sitting on the driveshaft. I put them together with wire butt connectors and all is good now.
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#8
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Re: Downstream O2 Sensor Help
Quote:
Pretty sure it's 12-volts to the heater |
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