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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
Walt White Coupe
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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
Mnfamilyguy2020
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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
Walt White Coupe
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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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      04-21-2022, 02:30 AM   #9
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Has anyone looked at this service bulletin?

https://static.nhtsa.gov/odi/tsbs/2015/MC-10147665-9999.pdf
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      04-21-2022, 08:03 AM   #10
Walt White Coupe
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I hadn't seen that. Sounds like I didn't have to replace the sensor after all. I went with the cheaper Bosch sensor and I suspect that is the same as the OEM sensor since they both look identical.
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      09-22-2022, 10:02 PM   #11
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Guys am getting 12B801 oxygen sensor heating after catalytic converter 2, function : internal resistance too high ,
I cleared the code 2 weeks back and it came back again , is there a video to do DIY the downstream sensor change ?
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      09-23-2022, 06:56 AM   #12
Walt White Coupe
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All you have to do to get to that sensor is remove the air filter box. I could not find any video that was specific to the sensor replacement. But google videos on spark plug replacement and that will show you how to remove the air filter box. Once that is done, the sensor is fully exposed and all you need is a socket designed for its removal.
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      02-12-2023, 05:45 AM   #13
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I'm also having this problem. 12B801 Lambda probe heating after catalyst 2, function; internal resistance too high. And also getting 12AC04 Lambda probe heating after catalyst 2; electrical: open circuit.

The thing is, when I bought the car at 90k KM I replaced all 4 O2 sensors, so I know the sensors are pretty much still brand new since I only just crossed 100K KM. And funny thing is the car used to throw that same code with the old sensors.

The code is intermittent and only came back around at around 98K (might've seen it once or twice before that too). But it's more stubborn now and if I erase the code it comes back pretty quick.

I'm starting to think maybe its the socket or wiring, possibly heating/melting. Anyone had problems with the O2 sensors wiring?
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      02-12-2023, 08:48 AM   #14
Mnfamilyguy2020
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Take a look at this.


https://static.nhtsa.gov/odi/tsbs/20...60281-9999.pdf
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      02-12-2023, 12:26 PM   #15
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Quote:
Originally Posted by Mnfamilyguy2020 View Post
I saw that, but that seems to be for 2014 model produced in 2013. Mine is 2013 model produced in 2012 and I don't have any CEL/emissions malfunction light on. I've already replaced the old sensor with a new one about 10K KM ago, so I can't believe it would already dead. Which is why I'm wondering if it may be a wire issue?
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      02-14-2023, 06:40 AM   #16
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UPDATE: Since I replaced mine I have not gotten a "Check Engine" or sensor error. Before I replaced the sensor, I detected an extremely light engine vibration at idle through the steering wheel at idle. That also disappeared right after changing the sensor.
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      06-21-2023, 06:32 AM   #17
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Getting intermittent 12B701 error code. Anyone know if this is the driver or passenger side?

Since it is a 2016, it is not covered by the SB above.

TIA

L


Last edited by Luftpost; 06-21-2023 at 06:34 AM.. Reason: Grammer....
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      06-21-2023, 07:59 AM   #18
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[QUOTE=Luftpost;30238888]Getting intermittent 12B701 error code. Anyone know if this is the driver or passenger side?

Since it is a 2016, it is not covered by the SB above.

TIA

L

The more detailed info at BMWfault.codes also does not say which side it is. Seems odd.
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      06-21-2023, 10:30 AM   #19
Walt White Coupe
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After you remove the air filter housing you should be able to access the wiring connection to both the left and right sensors. I think it's a 4 pin connector. You could measure resistance and see if it's over 5000 Ohms for either side to see which one is bad.

Once you have the air filter housing off, it's pretty easy to replace the sensor. It might make sense to just buy a right and left one and replace both at the same time. I'd buy the cheaper Bosch sensor because it looks identical to the factory part and suspect that is what the factory part is.


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      06-21-2023, 06:05 PM   #20
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Thanks Walt, I will do just that. Had it all off earlier today for inspection and cleaning. Very simple and easy to get to.

L
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      06-22-2023, 02:21 AM   #21
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Just make sure you buy the correct Bosch sensor. FCPEURO has it wrongly listed. If you have a N63TU you need to get the Bosch 0 258 010 435 for the downstream sensors and not the 0 258 006 755 listed on FCPEURO. Those are for the original N63 engines (2012). This might be why some people are having overheating/resistance too high and intermittent problems with these downstream sensors.
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