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Thread: Non vanos headers on vanos engine o2 sensor issues

  1. #1
    Join Date
    May 2020
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    Phoenix, Arizona
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    11
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    E39 540i

    Non vanos headers on vanos engine o2 sensor issues

    Earlier this year I bought a 6 speed 540i for under 3k, ran like crap because of two bent exhaust valves. Ultimately I pulled the engine and sourced a 60k mile engine with 3 month warranty. My originally cats on the manifold are completely garbage and clogged. I have an extra set of headers and mid pipe off a non vanos 540. Long story short, pre cat o2 sensor harness is WAY too short to reach the connector. Is it safe to cut and solder additional wire to extend it? I know the header swap has been done, but have found no information about the pre o2 sensor location. Any information is appreciated.

  2. #2
    Join Date
    Jan 2007
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    Atlanta, GA
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    2019 Silverado 2500
    I don't see why lengthening the wires would cause a problem.
    ASE and BMW Master Certified Technician

  3. #3
    Join Date
    Jul 2011
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    Arlington, VA
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    2018 BMW M240i
    I used to buy a generic Bosch oxygen sensor for my old 1985 325e. Iíd then cut the connector and some of the old cable from the old sensor. Iíd then solder the new sensorís cable onto the old sensorís connector.

    Some tips:
    1. Cut the wires old and new wires to different lengths so that the solder joints are staggered.
    2. Use shrink tubing for each individual solder joint.
    3. Use a lighter to shrink the shrink tubing.
    4. Cover the solder jointsí shrink tubing with fabric electrical tape (not plastic tape or shrink tubing) because of the heat.

  4. #4
    Join Date
    May 2020
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    E39 540i
    Lengthening the o2 will change the resistance going through the wires. The sensors work by creating their own voltage, changing the wire length may or may not effect how the engine will run. But thereís no other way around. Im going to have to do it, seems like itís the cheapest route, besides maybe a tune.

  5. #5
    Join Date
    Jan 2007
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    2019 Silverado 2500
    If done correctly, the increase in resistance will be negligible.


    Sent from my iPhone using Tapatalk
    ASE and BMW Master Certified Technician

  6. #6
    Join Date
    May 2020
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    Phoenix, Arizona
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    My Cars
    E39 540i
    So what I ended up doing was cutting some of my bad o2 sensor harness (upstream) and cut, spliced, then soldered. No issues with ~800 on the new swap.

    Grey goes to Grey, Black goes to Black, and thereís two identical white wires. I found that it doesnít matter which white wire goes to which. Iíve tested both and read the same exact values on Live data.

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