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Thread: Keep getting p0040 code...

  1. #1
    Join Date
    Mar 2012
    Location
    Fort Myers, FL
    Posts
    20
    My Cars
    2004 BMW 330ci coupe

    Keep getting p0040 code...

    I researched it and it sounds to me like its saying my wiring is swapped. Could there be another reason I'd be getting this code? If they are swapped, how do I know which one are swapped?

  2. #2
    Join Date
    Oct 2005
    Location
    Saint Petersburg, FL
    Posts
    4,559
    My Cars
    2001 330i Sport
    Did you recently mess with those connections? If so, then disconnect and reconnect them in the right spot. Not sure how to tell which is crossed, except just looking at them.

  3. #3
    Join Date
    Mar 2012
    Location
    Fort Myers, FL
    Posts
    20
    My Cars
    2004 BMW 330ci coupe
    Where can I unplug the the harness instead of removing the sensors? Are the harness' accessible?

  4. #4
    Join Date
    Oct 2005
    Location
    Saint Petersburg, FL
    Posts
    4,559
    My Cars
    2001 330i Sport
    I know the pre-cat sensors are easy to get to, at the top of the engine, the rear one may be tricky. The post-cat ones though, not sure, you'll just need to follow them, but they are accessible...

  5. #5
    Join Date
    Mar 2012
    Location
    Blackwood, NJ
    Posts
    232
    My Cars
    96 Z3/ 04 325/ 11 X328
    It means you have O2 Sensor Signals Swapped Bank 1 Sensor 1/ Bank 2 Sensor 1.

    what i get from this is:
    there are two o2 sensors right next to each other upstream and downstream and you plugged the sensor in the wrong socket. try switching the plugs?

  6. #6
    Join Date
    Jun 2013
    Location
    Durham, Ontario, Canada
    Posts
    198
    My Cars
    04 330Ci
    I just replaced my VCG and am now getting this code. I believe it may be the harness on the top of the engine.

  7. #7
    Join Date
    May 2018
    Location
    Chicago,IL. USA
    Posts
    19
    My Cars
    2006 BMW 750i
    I thought I should share my experience of my P0040 code. My car is a 2006 BMW 750i, E65. I had recently had my Transmission replaced by a shop. Long story short, they had crossed the wires for the upstream O2 sensors and I started getting a P2197 code. So I changed the sensor on the driver's side. The thing is I didn't notice the crossed harness because the wire casing where the sensor harness sits in was even crossed but if looking you wouldn't notice it, I knew I had installed the new sensor correctly but started getting the P0040 code. After searching Google the code was stating that "P0040 – Oxygen sensor signals swapped, bank 1 sensor 1 /bank 2 sensor 1". So I went a had and tried unswapped what they did and then NO WAS I GETTING ; misfires( yes P0040 causes misfires, car idle roughly and MIL Status On) or engine light or misfires . But now no more issues. So if recently had work done on your car and get this error P0040, go back and examine what they may have did or take it back to whomever did the work last and tells them to retrace their work.

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