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      03-01-2018, 08:14 PM   #1
Erik-AA
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DIY 128i O2 exhaust oxygen sensors

M 2010 128i is throwing repeated oxygen sensor codes. Not surprising at over 130k miles. To my surprise there is no guide to this that I can find in the forum.

I'll take photos and make a DIY guide if there isn't already one. But before I dive into it can anybody help me out a bit? I can't tell from the online info and the parts vendors whether the car has 2 or 3 or 4 sensors? Upstream for 1-3 and another upstream for 4-6? One or two downstream? I saw something about this being a big job on 135i, involving removing steering rack etc. Is that so for 128i too?

I'm inclined to replace them all while I'm in there since I'm in the right mileage range for them to fail and they're not that expensive. But the codes I'm getting are for downstream (after the cat) sensors and if the upstream sensors are a lot harder to get to I might leave them for now.

Thanks in advance for any advice!
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      10-16-2018, 02:50 PM   #2
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O2 sensor

Erik,

Did you ever replace those O2 sensors? Mine is doing a similar thing.

AD
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      10-17-2018, 09:56 AM   #3
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I have not tackled this on my 128i and do not currently have codes indicating an issue but I have avoided replacing the O2 sensor on other cars because of difficulty getting them out on prior cars. If you car doesn't get the O2 sensor signal, it has to resort to backup values to set the air fuel mixture. That can affect mpg and power. But the car will run. Usually it is not a complete loss of signal, the O2 sensor works most of the time, just not all the time.

If it is not rusted in place and you can get to it, it might not be a bad job. If it is rusted into the exhaust manifold and inaccessable, it can be pretty difficult. Can you see it?
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      02-20-2020, 04:03 PM   #4
Erik-AA
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I haven't done it yet. Too busy and the light mostly stays off. I did verify that there are four sensors, two (barely) visible from under the hood on the exhaust manifold, and two under the car after the cats. None of them look that easy to get to.

The exhaust system itself is good quality stainless steel, but some of the fasteners are another issue. The flanges and bolts that connect the back of the cats to the rest of the exhaust are very rusty. If any of the exhaust system needs to be taken apart to get to things, this is not going to be a fun job.

So being lazy and over-committed, I am putting it off.
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      02-20-2020, 06:20 PM   #5
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I just recently did mine on a 135i. Not that bad, don't have to remove anything but the belly pans. And I did have to cut the open end of a 7/8" wrench to about 6" long to get the room to turn the sensors. The 2 fronts or upstream ones are the ones that mostly go out. I'm guessing a 128 is similar in that area.
Definitely spray them with penetrating spray too
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      02-21-2020, 04:27 PM   #6
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If it helps....here is a pic of where they are in the OEM manifold. This was when I was installing headers.
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      05-17-2020, 07:55 PM   #7
Erik-AA
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I just did the two downstream ones on my 128i. It was easy, all I had to remove was the plastic belly pan. I didn't even need to use my O2 sensor socket. A 7/8" or 22mm open end wrench worked fine. My sensors weren't too tight though, if they are super tight a box end or socket is a better bet.
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      11-22-2022, 11:41 AM   #8
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How many O2 sensors on a 128i?
I thought there were 2, one for each set of 3 cylinders
Correct?
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      11-22-2022, 12:05 PM   #9
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... and to follow up, now I think there are 4 oxygen sensors
If only one is causing a SES error on dash, is that the only one I need to replace?
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      11-22-2022, 12:22 PM   #10
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There are indeed 4: https://www.realoem.com/bmw/enUS/sho...10#11787558055.

Sorry, don't know if you can somehow tell which one(s) is causing the code without trial and error.
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      11-22-2022, 01:23 PM   #11
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Thanks Almuliman
Anyone know how difficult the upstream and downstream fronts are to replace?
#s 1 and 2 in diagram . . .

https://www.realoem.com/bmw/enUS/sho...10#11787558055
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      05-02-2023, 03:50 AM   #12
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Quote:
Originally Posted by Erik-AA View Post
M 2010 128i is throwing repeated oxygen sensor codes. Not surprising at over 130k miles. To my surprise there is no guide to this that I can find in the forum.

I'll take photos and make a DIY guide if there isn't already one. But before I dive into it can anybody help me out a bit? I can't tell from the online info and the parts vendors whether the car has 2 or 3 or 4 sensors? Upstream for 1-3 and another upstream for 4-6? One or two downstream? I saw something about this being a big job on 135i, involving removing steering rack etc. Is that so for 128i too?

I'm inclined to replace them all while I'm in there since I'm in the right mileage range for them to fail and they're not that expensive. But the codes I'm getting are for downstream (after the cat) sensors and if the upstream sensors are a lot harder to get to I might leave them for now.

Thanks in advance for any advice!
Check out REALOEM.com click enter bmw catalog, enter last seven of vin into vin box, click search your specific model will show up, scroll down and click browse parts, you can find all the specific parts subcategories, illustrated parts breakdowns, part numbers and part nomenclature, this will help you a lot with every project you do on your bmw.
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      05-02-2023, 03:56 AM   #13
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Quote:
Originally Posted by Petro135 View Post
I just recently did mine on a 135i. Not that bad, don't have to remove anything but the belly pans. And I did have to cut the open end of a 7/8" wrench to about 6" long to get the room to turn the sensors. The 2 fronts or upstream ones are the ones that mostly go out. I'm guessing a 128 is similar in that area.
Definitely spray them with penetrating spray too
It’s always highly recommended to replace all 02 sensors at the same time, in short the result of not replacing them all can be catastrophic. There is also such a tool as a o2 sensor socket first the connectors must be disconnected and then you can use a ratchet with an extension to easily remove the o2 sensors, if they are seized in, use PB blaster to help break them loose, spray a conservative amount on the thread area, let soak for a minute or two, wipe off residual fluid, use a breaker bar with socket and extension to torque it loose, ratchet off after that, very easy this way!
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      05-02-2023, 04:00 AM   #14
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Quote:
Originally Posted by jdt10768 View Post
... and to follow up, now I think there are 4 oxygen sensors
If only one is causing a SES error on dash, is that the only one I need to replace?
There are bank 1 and 2, upstream and downstream, total of 4 o2 sensors, damn SULEVS are a nightmare. You must replace all o2 sensors at the same time, this is highly recommended, when you only change one the debris from exhaust will be read differently then the other sensors and can cause a myriad of issues with bmws because of their overkill sensitive monitoring system.
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      05-20-2023, 09:16 PM   #15
Erik-AA
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My scan tool told me which ones had trouble, upstream vs downstream, the only trick was figuring out bank 1 vs bank 2. So in my case it was downstream bank 1 and I replaced both of them because it's easy and if one was bad the other was probably close to bad. The job was easy. That was thousands of miles ago and so far no issues with the upstream sensors. I only have 183k miles on the car. :-)

I suppose if you have a code on an upstream sensor it might make sense to do all four as long as you are in there,time is more valuable than the parts cost. For me replacing just the downstream sensors worked fine.
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      05-30-2023, 02:04 PM   #16
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I am getting age related codes for one oxygen sensor. Fortunately I have another year left on the SULEV warranty, so I will get it fixed when the do the PCV heater recall.
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