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Old 08-06-2013, 09:53 AM   #1
Join Date: Jun 2013
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Oxygen Sensor assistance

2005 LJ, 4.0

Well, at around 106k miles I got my first check engine light P0153 code. Figured I would replace all 4 oxygen sensors. The only ones in stock were Bosch. Well, about 2-days later same code popped up. Replaced a couple of the sensors twice same code. Performed the TSB 25-001-07 rewire and same code.

So, I bought new NKT sensors. All seemed fine for a day. Now, same stupid code.

So, looks like my issue is NOT the sensors. I recently had the rig into the muffler shop for a leaky muffler. May have an exhaust leak. I know on my wife's old Grand Cherokee with a 4.0 that the exhaust manifolds had an issue with cracking. Does the 2005 4.0 have the same issue? Where would you start looking for an exhaust leak?

I assume that if this is not the case, I look at electrical. Thoughts on where to start?


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Old 08-06-2013, 10:34 PM   #2
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Start with the cat. O2 sensors are above the cat. Most people seem to think that it means the O2 sensor is malfunctioning. Even the dealership changed mine. I came to find out that the O2 sensor was working as it should and it informed me of the problem with my cat. The cat is much more sensitive than the O2 sensor because it is made of ceramic(I.E. glass) inside. If the cat is going bad, you will know in time. Eventually it will break down completely and you will hear lots of broken glass sounds inside it when you tap or shake it. Your performance will suffer, you might get stalling, difficulty switching gears, improper high revs, and I've heard that engine fires have happened(Backfiring), from the clogged exhaust system. Tap, or shake the cat and see if you hear broken glass like sounds inside it. My guess is that your cat is going bad, and your O2 sensor is giving you fore warning. I imagine this is common in vehicles like Jeeps which take a lot of jostling in off road excursions.

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Old 08-07-2013, 02:27 PM   #3
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I am really hoping it is an exhaust leak. I have a slight tap coming from the driver side engine bay. Only happens under load (not while parking).

This weekend I will put my shop vac hose (connected to the exhaust side) into my tail pipe and hit the whole thing with soapy water. IF I am lucky it will be a simple fix...I hope...
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'88 Grand Wagoneer (SJ) / 360 / TF727 / NP229 / DANA 44 (2.73)
'05 Wrangler Unlimited (LJ) / 4.0L / NSG 370 / NV231 / DANA 30-44 (3.73)
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Old 08-07-2013, 02:33 PM   #4
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yes the 4.0s are prone to having cracked manifolds, could very well be the issue.
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Old 08-07-2013, 07:40 PM   #5
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Yeah not always an O2 sensor when you have that code. Gets folks into trouble as they think it's the sensor, when in fact it can be quite a few things that will set the code.

Like mentioned, an exhaust leak can set it, bad wiring to the sensor, inlet air leak, even a faulty MAF sensor can cause it. And yes even a faulty O2 sensor.

But what I'm getting at, don't jump the gun and throw parts at a problem. Can get expensive if you guess wrong. There is a diagnostic flow chart for each code, follow it and it will lead you to the correct fix. Could be something as simple as a loose fitting ahead of the MAF. Replacing the O2 sensors isn't going to correct that.

The code tells you what part of the system is acting up, in this case it's telling you that the fuel mixture is not being adjusted properly or at a normal amount of times when the engine is in closed loop.
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Old 08-07-2013, 08:06 PM   #6
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The exhaust flange bolts on the converters are known to loosen.

The code indicates that the sensor response is slow. Causes could be the wiring, exhaust leak, O2 sensor.
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Old 08-07-2013, 08:14 PM   #7
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I had the same issue and the same code with my 06 LJ. Replaced the manifold gasket and that took care of it.
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Old 09-05-2013, 10:48 PM   #8
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I have pretty much the same problem only on my 03 and I get the rough starts occasionally though. Glad I found this thread. I like the idea of the shop vac reverse, and soapy water to look for a leak. Will a gasket leak show up with this method too? I also wasted cash replacing sensors. (Also had a mechanic say it was a vacuum leak and want to charge me >1k to repair it.)

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