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Old 07-07-2013, 08:41 AM   #1
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PO138 Code - Which Oxygen Sensor?

2000 Tj, 4.0, new crate engine pulled a PO138 code, Oxygen Sensor, Bank One, Sensor two. On mine I have a split exhaust on the 4.0, one sensor on the "Front" pipe and one on the back. I understand those sensors are the same, so I'm trying to determine which one is the one that needs to be replaced - Bank one, Sensor two. "Front" one or the back one?

Also, at the parts store they list two sensors "Upstream" from the cat, and one behind, they show a sensor on the cat itself right before the muffler, there is no sensor on mine, on the cat itself, and I don't see any wire connector down there that would go to it. I've owned the truck for ten years from 32,000 miles and it's never been replaced.

I also pulled a PO445, large vacum leak, I can't find anything, but I don't have a stock gas cap, so I'm going to start there

Any insight would be greatly appreciated, I don't want to spend the money and replace the wrong sensor.

Thanks

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Old 07-07-2013, 12:09 PM   #2
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Bank One is the half of the split header closest the front of the engine, Sensor Two is below the pre-cat. Sensor one is closest to the head. The parts store diagram is simply outdated/incorrect for your model... imagine that. Brand-wise, try to get an NTK and by all means avoid installing a Bosch 02 sensor which just doesn't work well in a Jeep engine.

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Old 07-07-2013, 04:10 PM   #3
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OK
Thanks for the reply,

SO

Looking at the left side of the engine, there's a sensor to the left, towards the front of the engine, then another to the right, towards the back side or towards the firewall, for Bank one, sensor two, which should I replace, the one towards the front of the engine, or the one towards the firewall?
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Old 07-07-2013, 06:13 PM   #4
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Bank One is the bank nearest the the front. Sensor Two of Bank one is the one under the catalytic converter closest to the front of the engine.
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Old 07-08-2013, 06:47 AM   #5
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Gotcha, Thanks!
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Old 07-16-2013, 09:00 AM   #6
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OK, I replaced my 02 sensor, bank one, sensor 2 per the PO138 code front pipe, down below the cat. The Check engine light went out, it does seem to be running better, but still feels like running on 5.5 cylinders. This is a new 4.0 crate engine in a 2000 TJ. Without a CE light I'm not pulling any codes, so I'm wondering if it just needs miles to clear up, or how to find whats causing the continued problem. I'm still getting a smell under a load

This is really starting to aggrivate me!

Thanks

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