What are typical O2 sensor values?

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Pathy17
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Joined: Tue Dec 05, 2017 11:22 am

What are typical O2 sensor values?

Postby Pathy17 » Thu Dec 07, 2017 10:59 pm

Got an '06, SE Pathfinder, 135k miles periodically throwing a catalyst code. Doing due diligence, I checked the O2 sensors. The values that I'm seeing on my scanner aren't what I expect. If these were on my Chevy or Pontiac's, I'd say that I had 2 bad sensors with a 3rd one on the way out. It doesn't seem to bother the Pathfinder, getting around 15 mpg city and 19 hwy.

No other codes, just a cat efficiency code (Bank 1 if I remember right) that clears itself after a few days.

Here are the O2 values:
Bank 1 - S1 = .290-.310
Bank 1 - S2 = .07 - .79 (this one's range is what I would consider normal)
Bank 2 - S1 = .590-.610
Bank 2 - S2 = .25 - .66 (starting to fail?)

Based on past experience, when an O2 fails, they flat line. Neither B1S1 and B2S1 are flat line, but they don't move much off of it either. Slow bump up, flat for a while then drop down. Very slow movement. Much slower than what I've seen on other vehicles.

Can anyone definitively say what the acceptable ranges are for the O2 sensors on this 4.0 motor?


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smj999smj
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Postby smj999smj » Fri Dec 08, 2017 12:32 am

You won't notice much movement on the front oxygen sensor readings because the are air/fuel ratio sensors rather than conventional oxygen sensors, which is what the rear sensors are. It's very difficult to determine if air/fuel ration sensors are faulty even with a scan tool that allows you to view data streaming from the ECM. I've also noticed that when readings are posted on the front sensors by people, it is typical to have uneven readings when comparing left to right banks. If there is an open circuit, the ECM will go into "O2 sensor fail safe" and will generate 0.33 volts which is what can be measured on the scan tool and what is used as a reference voltage until the issue is fixed (obviously the CEL will illuminate and a code will be triggered). Usually if you get a P0420 or P0430 code and there are no other codes nor any exhaust leaks nor vacuum leaks, it's the upstream catalytic converter on that respective bank that has failed. This is pretty common, seemingly more so for 05-07 models.
My 08 Pathy still has all her original catalytic converters with 220,000 miles on them. However, on my 06 Pathy, the left-front converter failed and was replaced with a Nissan converter at 84,000 miles and again is triggering an intermittent P0430 code, now at 172,000 miles. The right bank was replaced with a Walker converter at 150,000 miles and so far, so good.


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