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      01-23-2021, 11:01 PM   #1
Walt White Coupe
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Engine Problem 12B801: Oxygen Sensor Resistance Too High

So I ran a "Carly" diagnostic today and while I'm getting no indication on the dashboard of an engine/emission problem, it came up with downstream Oxygen Sensor Cat 2 internal resistance too high. And "12AC04" downstream Oxygen Sensor Cat 2 electric cable disruption.

So it sounds like to me that the problem is probably with the connector that the downstream oxygen sensor on the drivers side connects to and may be the culprit and needs looking into.

I've looked through numerous youtube videos but I can't find any about how to replace the #2 downstream oxygen sensor in my 2013 650ix with the N63B44TU engine.

Can anyone point me to a procedure on line for replacement so I can see how complicated it is and whether I should try to replace the sensor myself. I figure if I get down to it, I might as well just replace the sensor rather than dicking around with it.

And just for starters, do you attack it from the top or from the bottom of the engine.

Thanks in advance for any help you can provide.
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      01-24-2021, 07:59 AM   #2
Mnfamilyguy2020
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I’ve experienced some wonky O2 sensor issues. (I posted a little over a year ago here) My first hint that the sensors themselves might be an issue was this: https://static.nhtsa.gov/odi/tsbs/20...60281-9999.pdf

My car was outside the year covered here, but after some good inside scoop from the shop foreman at my Dealer, he shared that these sensors get “fouled” after about 50k on the N63TU and eventually fail.

Super easy to replace. Pull the engine cover, then the air filter boxes and your O2 sensors present themselves very clearly.

Last edited by Mnfamilyguy2020; 01-24-2021 at 08:28 AM..
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      01-24-2021, 11:27 AM   #3
Walt White Coupe
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^^^^
Thank you so much for that helpful information. Do you know if a faulty downstream O2 sensor should cause an "Emissions" warning on the dash display?
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      01-24-2021, 11:52 AM   #4
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Mine eventually did.
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      01-25-2021, 01:36 PM   #5
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I don't think I'm going to attack this until I get a emissions warning on the dash.
Any suggestion about getting the exact BMW Lambda replacement at ~$190 or the Bosch unit at ~$60.

Last edited by Walt White Coupe; 01-25-2021 at 10:09 PM..
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      01-26-2021, 09:14 AM   #6
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I actually found out the sensor was going through some other strange behavior the car was having. These sensors especially the one you’re talking about downstream affect timing fuel trims etc., the first indication I had a problem was in the very cold Minnesota weather at high-speed acceleration I noticed a momentary hesitation but no CEL. I then started logging ignition timing and fuel trim data and noticed some really odd things. The car was still under warranty so I took it in and they literally went crazy on it, replacing injectors coil‘s turbo parts etc., later I actually found the failing O2 sensor again through real time data logging. I eventually got a super knock code and CEL, which is a potentially disastrous problem.

My suggestion is to replace it with OEM. It’s definitely causing you other problems you’re not seeing, certainly lower fuel economy.
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      03-01-2021, 08:41 AM   #7
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So this is what I've learned about the diagnostic saying that my O2 sensor after the cat converter has internal resistance that is too high. That aft sensor has no effect on engine fuel management or any other operating functions.

The O2 sensor before the cat converter is the important one for controlling those functions. Essentially the sensor after the cat converter is used to determine if your cat converter is functioning as designed. So, I'm in no hurry to replace it.
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      03-01-2021, 09:53 AM   #8
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Quote:
Originally Posted by Walt White Coupe View Post
So this is what I've learned about the diagnostic saying that my O2 sensor after the cat converter has internal resistance that is too high. That aft sensor has no effect on engine fuel management or any other operating functions.

The O2 sensor before the cat converter is the important one for controlling those functions. Essentially the sensor after the cat converter is used to determine if your cat converter is functioning as designed. So, I'm in no hurry to replace it.

This was super helpful to me:

https://us.autologic.com/news/fuel-t...-faults-part-2

Try data logging your fuel trim in real time after warm up. Depending on your scanning tool you should also be able to graph real time O2 Sensor data and compare them from each side, this is when it was plain as day to me.
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