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EML been on for six years with no apparent problem but MOT due.

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by mainbunny, Mar 17, 2019.

  1. mainbunny

    mainbunny Active Member

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    Your Mercedes:
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    Hi guys, have read the codes pertaining to the EML, P0141, P0130, P0101, and P0136...Have had the O2 sensors both replaced, twice in the past and the MAF three times, cures the EML problem but comes back on after a few weeks, of course with the MOT due it would be a fail straight away. Any ideas guys?..It's a C200 2002...thanks in advance. Oh, it has been into the Mercedes dealers where they stripped the engine down for a stalling problem at the time, that cost over a grand to repair, they also put in the last MAF, again it was alright for a couple of weeks before the EML returned.

    Thanking you,
    Colin...(Mainbunny).
     
  2. Oldspanners

    Oldspanners Senior Member

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    If your engine is a M271 have you had problems with oil wicking into the wiring harness through the cam magnets as that can throw up problems with oil getting to the O2 sensors and ECU?
     
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  3. OP
    mainbunny

    mainbunny Active Member

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    Ahhh right, not as far as I know but shall look into it..Thank you Oldspanners and thanks for the speedy reply..
     
  4. Oldspanners

    Oldspanners Senior Member

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    Hint, after the initial post if you reply to the answer and not a new post, there is an alert posted so as the person answering knows, otherwise you can wait a long time for a reply.
     
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  5. OP
    mainbunny

    mainbunny Active Member

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    Thanks for the heads up Oldspanners..You guys are brilliant..
     
  6. OP
    mainbunny

    mainbunny Active Member

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    Hi again, just an update, apparently doesn't appear to be an errant oil drip here but I do have the app Torque lite on my phone so cleared the fault codes and each time they came up it was only immediately (after 0.5 second) after starting. Every time this time it was just the one code, P0141, O2 Sensor bank 1 Sensor 2...The fact that the code comes up on keyturn is interesting, as in it doesn't have a lot of time for the CPU to have a think about it...The other codes haven't returned, yet anyway, I'm thinking of waiting for the MOT day and have the sensor replaced then, (Just in case it returns at a later date), that's indeed if it is that causing it, it has been replaced before (allegedly)..So next question, which make aftermarket sensor do you guys recommend?...Thanks again for all the help..
     
  7. Oldspanners

    Oldspanners Senior Member

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    Your Mercedes:
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    P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)
    Looks very much like your heater circuit is faulty.
    The after cat sensor has a heater circuit to help it on start up to read the correct levels.
    This can "burn out", it is easy to test with a multi meter. There should be two of the four wires the same colour measure ohms across them it should be low (from memory 10 or so) don't touch the others on resistance setting.
    Edit. I'd go with a Bosch, I got one on ebay for £40.
    Oh, have a good look in the connector for any sign of oil as the oil actually "wicks" through the copper strands of the wire from the cam magnets which may need changing or at least blockers fitted as it is not a leak as such.
     
    Last edited: Mar 19, 2019
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  8. OP
    mainbunny

    mainbunny Active Member

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    Thank you Oldspanners, is the heater circuit inside the sensor, as in change the sensor and you automatically change the heater cct.?
     
  9. Oldspanners

    Oldspanners Senior Member

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    Yes it's part of the sensor.
    Unplug it underneath the car by the LHS of the bell housing and test it from there.
    PS Best to reply to the post to give an alert.
     
  10. OP
    mainbunny

    mainbunny Active Member

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    I shall order a Bosch sensor and get it replaced by my usual little garage around MOT time in a few weeks..Will let you know the outcome then..Really appreciate your advice Oldspanners, thank you.
     
  11. umblecumbuz

    umblecumbuz Senior Member

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    One question.
    If a 2002 car has had the eml on for six years, and you are now concerned because its Mot is due, how did it pass its previous Mot's?
    If you simply scanned it each time to remove the eml, why can't you do it this time?
     
  12. OP
    mainbunny

    mainbunny Active Member

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    Hi Umblecumbuz, it previously got through the MOT with the light on with just an advisory to highlight that there was some sort of problem. I had both sensors and the MAF replaced previously but I bet they weren't Bosch ones, maybe cheapy ones.
     
  13. OP
    mainbunny

    mainbunny Active Member

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    Ahhh, last question (maybe), is this bank 1 sensor 2 pre or post cat please?
     
  14. umblecumbuz

    umblecumbuz Senior Member

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    Then, as you say the eml has no effect on the car's performance, why not get a code reader to douse the light just before the Mot.
    It will come back on later, but you will have passed the Mot and it will have cost you next to nothing.

    I disconnect the egr valve on one of my cars by simply unplugging it. The eml shows up, but I reconnect the valve just before each Mot, and douse the light with a scanner. Not a problem.

    No point just swapping parts in the hope that you will eventually hit the right one. That's the road to automobile bankruptcy.
     
  15. OP
    mainbunny

    mainbunny Active Member

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    That's indeed exactly what I would do, unfortunately the eml comes on every time I crank the engine after dousing it...Must admit I was tempted to stand outside the mot station and keep dousing the light with my phone via Bluetooth.
     
  16. OP
    mainbunny

    mainbunny Active Member

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    So is 'bank 1 sensor 2' pre or post cat please?
     
  17. umblecumbuz

    umblecumbuz Senior Member

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    With no ill effects, are you sure this isn't a wiring problem rather that a sensor fault?
     
  18. OP
    mainbunny

    mainbunny Active Member

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    No, I'm not sure, maybe I'll just leave it to the guys to diagnose now you've mentioned it..It had to be the one under the car didn't it?..Thank you my friend.
     
  19. Oldspanners

    Oldspanners Senior Member

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    You're replying to yourself now.
    It's the after/post cat sensor a four wire and has a heater element that's why the code is, P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2). This can be caused by a simple failure or as a result of oil wicking into the wiring harness on the M271 engine. Changing it without fixing the oil problem will result in another failure and lots of other odd problems.
     
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  20. Oldspanners

    Oldspanners Senior Member

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    He says the code comes up immediately as P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2) which would happen if the heater circuit is faulty but I'm advising him to look for the oil wicking into the wiring harness from the cam magnets if it's the M271 engine.
     

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