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Thread: O2 sensors issue

  1. #1
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    O2 sensors issue

    Hello,
    I have an issue with my 2012 530i. Basically all four O2 sensors are giving fault codes, in addition to a mixed up code. All details can be found in the following image:
    https://ibb.co/m7W54d

    The car is idling fine with no issues. Just a check engine light.
    Thabks in advance

  2. #2
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    You don't think it's odd that the before and after cat readings are opposite AND out of range? That seems weirder than the unknown "mixed" message (no pun intended). I'm pointing this out in case somebody more knowledgeable does a quick read and misses it. Wish i could be of more help.

    - - - Updated - - -

    And my post count on that last msg is ominous...you might as well give up now.

  3. #3
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    Given the forum combines msgs, the ominousness actually applies to that msg. ("Ominousness" is a real word? Who knew?)

    - - - Updated - - -

    If the sensors were backwards, your engine would run like poop.

  4. #4
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    666 what could go wrong lol! Thanks for the reply. This thing is driving me crazy. Besides, I have no idea if sensors were mixed up as I got the car about a month ago.

  5. #5
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    Were the cats warmed up when you did your diagnostics?

  6. #6
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    Quote Originally Posted by HighandFast View Post
    Were the cats warmed up when you did your diagnostics?
    Yes. I erased the codes but they came back as expected some time later

  7. #7
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    Your sensor plugs are swapped. To diagnose and fix exactly what's happening, Hook up to a good BMW diagnostic computer, and go to live data. Cylinders 1-2-3 (front of engine) are bank 1. 4-5-6 are bank 2. Unplug sensor 1, before the cats. Make sure sensor 1 is what's no longer reading. If sensor 2 disappears instead, those two plugs are swapped.

    Now, do the exact same thing for the after cat (secondary) sensors, which is, after all, where you have the code for swapped sensors.

    On late model BMW's, like yours, the secondary sensors are also used to fine-tune fuel mixtures, so they can throw off the primary sensor's readings, even if only the secondary sensors are swapped.

    That said, always begin diagnostics with the primary (pre-cat) sensors.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  8. #8
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    Quote Originally Posted by bmwdirtracer View Post
    Your sensor plugs are swapped. To diagnose and fix exactly what's happening, Hook up to a good BMW diagnostic computer, and go to live data. Cylinders 1-2-3 (front of engine) are bank 1. 4-5-6 are bank 2. Unplug sensor 1, before the cats. Make sure sensor 1 is what's no longer reading. If sensor 2 disappears instead, those two plugs are swapped.

    Now, do the exact same thing for the after cat (secondary) sensors, which is, after all, where you have the code for swapped sensors.

    On late model BMW's, like yours, the secondary sensors are also used to fine-tune fuel mixtures, so they can throw off the primary sensor's readings, even if only the secondary sensors are swapped.

    That said, always begin diagnostics with the primary (pre-cat) sensors.
    I can't thank you enough! The pre-cat sensors were swapped! Everything runs perfect now.

  9. #9
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    Dang, I thought you were saying the sensors were swapped as in the connectors at the top of the engine. I was totally confused. I can say from experience that that would have caused you running roughness you couldn't miss, as in, runs like poop. I actually came back to this thread to see if you posted an update. Glad to hear it worked out. Let's see, how many of us has Chris pulled our heads from our asses to save the day, hmm. Many hundreds, if not well over a thousand.

  10. #10
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    Same thing, my friend. Swapped in the hole, or swapped at the plugs.

    This MIGHT cause the car to run like crap, or it might not. I depends on how differently the two banks are running.. This car is a lot different than an E36 or E46 -- it actually uses the secondary sensors to help tune the fuel mixtures. AND, it can post a code for swapped sensors.

    The same trick for diagnosing it will work on any age of car though, if you have a way to watch live data, you can see which sensor disappears.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  11. #11
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    Okay, then my ignorance is even greater than I knew—I need to study the electrical diagrams and own this information. It has stung me already, as I alluded to.

    I thought the connectors on top, if swapped, fed the post-cat sensors' data to the ECU's pre-cat port, and vise versa. What the OP did was swap the banks, or in less precise words, left to right, not front to back. No need to get into a long discussion here, I will definitely look it up so I understand.

    My car with the reversed sensors ran, but sometimes on acceleration and idling, it would run very rough, clearly misfiring. I remember it being smooth while cruising...but that was many years ago.

    (BTW, in that situation, I ended up going to a indi BMW shop and the tech couldn't make sense of what he was seeing. He showed it to me and the negative numbers I saw I immediately interpreted as meaning the O2 sensors reversed front-to-back. But I knew recent history on the car, so I had an unfair advantage.)

  12. #12
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    Quote Originally Posted by HighandFast View Post
    Okay, then my ignorance is even greater than I knew—I need to study the electrical diagrams and own this information. It has stung me already, as I alluded to.

    I thought the connectors on top, if swapped, fed the post-cat sensors' data to the ECU's pre-cat port, and vise versa. What the OP did was swap the banks, or in less precise words, left to right, not front to back. No need to get into a long discussion here, I will definitely look it up so I understand.

    My car with the reversed sensors ran, but sometimes on acceleration and idling, it would run very rough, clearly misfiring. I remember it being smooth while cruising...but that was many years ago.

    (BTW, in that situation, I ended up going to a indi BMW shop and the tech couldn't make sense of what he was seeing. He showed it to me and the negative numbers I saw I immediately interpreted as meaning the O2 sensors reversed front-to-back. But I knew recent history on the car, so I had an unfair advantage.)
    Actually you are right! I swapped "left to right" not "front to back"; and the same issue is back again. Can you advice me on how can I swap them correctly. I know you explained in your first post, but I don't really get it.

  13. #13
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    Quote Originally Posted by HighandFast View Post
    Okay, then my ignorance is even greater than I knew—I need to study the electrical diagrams and own this information. It has stung me already, as I alluded to.

    I thought the connectors on top, if swapped, fed the post-cat sensors' data to the ECU's pre-cat port, and vise versa. What the OP did was swap the banks, or in less precise words, left to right, not front to back. No need to get into a long discussion here, I will definitely look it up so I understand.

    My car with the reversed sensors ran, but sometimes on acceleration and idling, it would run very rough, clearly misfiring. I remember it being smooth while cruising...but that was many years ago.

    (BTW, in that situation, I ended up going to a indi BMW shop and the tech couldn't make sense of what he was seeing. He showed it to me and the negative numbers I saw I immediately interpreted as meaning the O2 sensors reversed front-to-back. But I knew recent history on the car, so I had an unfair advantage.)
    You are right! I swapped "left to right" not "front to back". I caused a confusion here sorry lol. So I know you explained in your first post there but still I don't get it. The problem came back again.
    Thanks in advance

  14. #14
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    Can you confirm the vehicle? I tried to look up a 2012 530i, and cannot find it. Not a 2002 530i, is it? Or a 2012 550i?

    What device are you using to read those codes? And what are the codes now? I see that you say the "pre-cat sensors were swapped".....which is NOT what the code said: The code said the post-cat sensors were swapped. Did you do the diagnostics of unplugging one sensor, and seeing which one went away on live data?

    If you didn't do the diagnostic look at live data, and you swapped the pre-cats sensor plugs, when you had a code for post-cat sensors being swapped, you probably now have aLL 4 sensors swapped.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

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