Where's O2 Sensor Bank 1, Sensor 2 located? - Jeep Wrangler Forum

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Old 09-04-2012, 07:24 PM   #1
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Where's O2 Sensor Bank 1, Sensor 2 located?

OK, I've got my Gearheadengine crate 4.0L in and it is running great. I did let the dealer get my CPS timed/adjusted. After about 30 minutes, the engine light came on and I quickly got to the nearest Autozone to have them pull the code. They pulled a P0138 code (voltage too high). Said it might be O2 sensor Bank 1, Sensor 2. According to the Autozone guy, that is the sensor aft of the catalytic converter. Problem is, I can't find any sensors or wires of any kind other than the two coming off the exhaust manifold on the drivers side of the engine. I have a 2004 Wrangler Sport 4.0L. Anyone have any idea where I can find O2 sensor B1 S2? I do not have the California version.

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Old 09-04-2012, 07:28 PM   #2
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P0138 (M) 1/2 O2 Sensor Shorted To Voltage Oxygen sensor input voltage maintained above normal operating range.

It is bank 1, downstream. If you do not have the "Cali" version, you should only have 2 sensors, the downstream one being after the main cat back by your muffler.

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Old 09-04-2012, 07:29 PM   #3
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Not positive on the newer ones but on the older models the Rear O2 sensor was right behing the converter.
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Old 09-04-2012, 07:36 PM   #4
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your engine has three catalytic converters on it. two are directly below the intake/exhaust manifolds, and the third is at the skid, by the transmission. there are four oxygen sensors...two upstream in the cast exhaust manifold, and two downstream after the mini-cats in the downpipe.

bank 1 is the front of the engine, sensor 2 is downstream.

so the code is for a voltage problem in the front downstream O2 sensor. either it's not plugged in properly, it's damaged/defective/worn out, or something is wrong with its location/position in the exhaust stream, causing a high voltage reading. in order to have this code thrown, the voltage needs to be way too high for a long period of time (like 1.5V for 5 minutes or something). this could also make the engine run lean.
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Old 09-04-2012, 07:46 PM   #5
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Unlimited, I don't have the Cali version so I only have two sensors on the down pipes. One on cyl 1-3 and the other on 4-6. Based on what you said, though, it is starting to make sense...When I hear aft of the Cat, I'm assuming it is the one just ahead of the muffler. I didn't realize there were two coming off the engine. I'm guessing then that I need to focus on the one forward of the two I have on the drivers side exhaust (the one on cyl 1-3)....
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Old 09-04-2012, 07:46 PM   #6
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Quote:
Originally Posted by UnlimitedLJ04
your engine has three catalytic converters on it. two are directly below the intake/exhaust manifolds, and the third is at the skid, by the transmission. there are four oxygen sensors...two upstream in the cast exhaust manifold, and two downstream after the mini-cats in the downpipe.

bank 1 is the front of the engine, sensor 2 is downstream.

so the code is for a voltage problem in the front downstream O2 sensor. either it's not plugged in properly, it's damaged/defective/worn out, or something is wrong with its location/position in the exhaust stream, causing a high voltage reading. this could also make the engine run lean as well.
I was going to add that, but he said he doesn't have the Cali version with 4 O2's. I kind of wonder though if he's saying he found 2 up front by the drivers side...

For the OP, if you look up from under the drivers side, does it look like this?

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Old 09-04-2012, 07:51 PM   #7
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Unlimited, I stand corrected...I do have four. I see the mini-cats as well. So Sensor Bank one, sensor 2 would be the lower one supporting cyl 1-3...Thanks for the help!
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Old 09-04-2012, 07:55 PM   #8
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Quote:
Originally Posted by bohanm
Unlimited, I stand corrected...I do have four. I see the mini-cats as well. So Sensor Bank one, sensor 2 would be the lower one supporting cyl 1-3...Thanks for the help!
Yep, you got it now. 1-3 are the closest to the front.
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Old 09-04-2012, 07:56 PM   #9
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HarryJeepGuy,

Sure does...Not sure how I missed the upper two...Guess I do have a California jeep after all. Thanks for the clarification and pic...
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Old 09-04-2012, 07:57 PM   #10
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Quote:
Originally Posted by bohanm
HarryJeepGuy,

Sure does...Not sure how I missed the upper two...Guess I do have a California jeep after all. Thanks for the clarification and pic...
No problem.
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Old 09-04-2012, 08:08 PM   #11
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Quote:
Originally Posted by bohanm View Post
HarryJeepGuy,

Sure does...Not sure how I missed the upper two...Guess I do have a California jeep after all. Thanks for the clarification and pic...
i think they stopped the california / non-california emissions separation in 2000. all the later models have three cats & 4 O2 sensors as far as I know. it's easier for a manufacturer to just make everything one way than sell a separate set of vehicles to one state....besides, what happens if you move to Comifornia for work? You'd have to redo your entire emissions system...
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Old 09-04-2012, 08:17 PM   #12
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...besides, what happens if you move to Comifornia for work? You'd have to redo your entire emissions system...
Not true.
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Old 09-04-2012, 08:46 PM   #13
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Came out no problem, went to put the new one in, and the damn cable connector doesn't match...must have given me the wrong one...BTW, I have a Bosch now, but read a couple of threads that people have had issues with them in Jeeps. Anyone have success with the Bosch, or should I go with Denzo?
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Old 09-04-2012, 08:51 PM   #14
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Unlimited...loved the Comifornia reference! Never heard that one before. Appreciate all the help, guys! Going to have to wait until the morning to get the correct sensor and hope that takes care of my P0138 code.
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Old 09-04-2012, 08:56 PM   #15
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After you get it replaced, you'll probably have to disconnect your battery for a while to get the code to clear. I usually let it go overnight.
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Old 09-04-2012, 09:51 PM   #16
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I found a half an hour did my light
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Old 09-10-2012, 11:19 AM   #17
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New O2 sensor seems to have done the trick on my P0138 code...However, after disconnecting my battery for 30 minutes to clear out the code, my security remote didn't clear the security lockout and my car wouldn't turn over (red light on dash flashing)...after a couple of panic minutes, I decided the remote battery may be dead. I replaced the battery in my remote and it cleared the security lockout. All good, and no damn check engine lights...for the moment!

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