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Thread: Code 12

  1. #1

    Code 12

    There has been some discussion on o2 sensors in various threads and didn't want to highjack them.

    On the weekend, car had check engine light come on with just code 12 which points to o2 sensor heater. After couple of days, code 2 came on as well which indicates bad o2 sensor. So, I was pretty convinced that I need to get a new sensor to fix both issues.

    Yesterday I cleared all the codes and now only code 12 is back. I am planning to order a new sensor and try it but wanted to see if anyone else had seen just the code 12 and found something else to be an issue e.g. a short or a grounding issue? On M104, it is easy to test the heater circuit since the connection is under the passenger side carpeting. On M119, the connector is underneath the car and that means waiting till the weekend to clear out the garage and lift the car up.

    thanks for any pointers.

  2. #2
    E500E Guru nocfn's Avatar
    Join Date
    Jan 2014
    Kingwood TX

    Re: Code 12

    If it were me with no records or a O2 older than 40k, I'd reset the codes and install a new sensor and move on.
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
    2014 E350 Cab 799/264

  3. #3

    Re: Code 12

    That's the plan. I ordered Bosch 13429 as discussed in many threads and will see what it does.
    The reason why I was particularly concerned with just code 12 is because on my 1995 E320, I saw the same symptom and it required a new ECU. Good thing one of the forum members has shipped me a unit and should be able to test it out as well.
    Will report back.

    Quote Originally Posted by nocfn View Post
    If it were me with no records or a O2 older than 40k, I'd reset the codes and install a new sensor and move on.

  4. #4

    Re: Code 12

    As I was getting ready to put in the new sensor, I saw that the existing one had loose connection (electrical end). Tightened it and car has been running without any codes since then. While I was there, I checked the wires coming from the ECU and confirmed that sensor heater circuit was outputting 14V.

    I will keep the sensor in my parts pile for now...
    Oh, and did get o2 sensor socket set from Oreilly for 48 hour rental.

  5. The Following 2 Users Say Thank You to mikeym For This Useful Post:

    gsxr (10-10-2017), Stevester 500E (10-10-2017)

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