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P2138 Throttle/Pedal Pos Sensor/Switch D/E Voltage Correlation

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by ncarey265, Jun 13, 2019.

  1. ncarey265

    ncarey265 Senior Member

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    Hi all again!

    Driving home from work and got the dreaded engine management light. Followed my messages that my collision prevention assist plus not working. Car went into limp mode even worse limb mode then I've experienced before.

    I plugged it in and got P2138 Throttle/Pedal Pos Sensor/Switch D/E Voltage Correlation. Were do I start with this and ideas/ help greatly appreciated.

    Car is 2014 w205 c220

    Thanks
    Neil
     
  2. Uncle Benz

    Uncle Benz Senior Member

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    Sounds like a throttle pedal fault to me. These are double safe by design. One potentiometer tracks up and the other tracks down. The output on one ranges 0-5v and the other 5-0v. The checksum of the two values should always add up to 5v. Something is wrong with yours.
     
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  3. OP
    ncarey265

    ncarey265 Senior Member

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    Would you suggest a new throttle pressure sensor fitting?
     
  4. Uncle Benz

    Uncle Benz Senior Member

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    I'd be looking closely at the throttle pedal itself. It is all housed in the one unit. You'll find it on the floor in the drivers footwell ;)
     
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  5. OP
    ncarey265

    ncarey265 Senior Member

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    what am I looking for in doing that then?
     
  6. Uncle Benz

    Uncle Benz Senior Member

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    If you have a diagnostic machine with live data you can look at the output of the pedal, check for any anomaly. If you don't it is a bit of a leap, but pedal faults are reasonably common.
     
  7. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    There is a common fault with these and a TIPs document, usually a new pedal, replacement wiring pins and an update of software. Effecting all the range.
     
  8. OP
    ncarey265

    ncarey265 Senior Member

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    Oh jeez looks like it's gone over my head lol

    So I have done an ecu reset not sure if this has worked yet as not been out in the car. I was thinking if this doesn't work to replace the throttle pressure sensor? As my research suggests this is 99.9% the problem.
     
  9. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Not really, like I said, there is an issue with throttle pedals across the range and 70% is wiring related. There is high resistance through the pins. So you need to replace the wiring pins and update the software. It could be the pedal, but its an expensive guess.

    It will be an Indy specialist job at the least.
     
  10. OP
    ncarey265

    ncarey265 Senior Member

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    After resetting my ecu and clearing the codes it's not come back on I'm hoping this has fixed it. I'll keep you posted.
     
  11. OP
    ncarey265

    ncarey265 Senior Member

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    This is idle readings
     

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  12. Oldspanners

    Oldspanners Senior Member

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    I think 50% throttle for idle is a bit strange.
     
  13. OP
    ncarey265

    ncarey265 Senior Member

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    Can anyone else expand on this? Is this not normal?
     
  14. ajlsl600

    ajlsl600 Senior Member

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    uninformed ,but if idle to full throttle is near 0-20%-100% then 50% at idle seems odd. someone, just about anyone in this case ! will be along who knows better.
     
  15. Oldspanners

    Oldspanners Senior Member

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    As Steve said there is a problem with throttle pedals and their connectors. 50% is obviously half throttle and not normal for idle, this is symptomatic of the problem. You could change the pedal assembly and find out the connectors are the problem, so unless you have a way of testing it it's a guess as to what the problem is.
    Here is a link to a WIS document https://mbwis.net/en/doc/7054324 check if it's your model I just had to guess.
     
    Last edited: Jun 14, 2019
  16. OP
    ncarey265

    ncarey265 Senior Member

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    Thanks for that I'll repalce the pedal assembly easy enough fix. Any idea were I can get one from? And how much I'm looking at to buy one? Thanks.
     
  17. Oldspanners

    Oldspanners Senior Member

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    Your Mercedes:
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    https://mercedes.7zap.com/en/eu/fg/car/
    Put your VIN in the link, go to Control and find the part number that fits your car then have a look on ebay or contact a dealer direct MB Grangemouth or Newcastle are usually helpful and Grangemouth may give you a MBO DISCOUNT.
    But this may not be the problem!
     
  18. OP
    ncarey265

    ncarey265 Senior Member

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    the image below is what it was showing before I even turned the engine on now that cant be right?
     

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  19. Oldspanners

    Oldspanners Senior Member

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    Certainly big trouble in the throttle area. You can try removing the pedal and cleaning the connector just to see if it makes any difference and prove that at least you are on the right track.
     
  20. OP
    ncarey265

    ncarey265 Senior Member

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    Would you say the pedal is certainly the problem based on those readings with the engine turned off? What's the other likely causes? Tps? And pedal fir what they cost I can just repalce both. If there no chance if could be something else.

    What would you suggest cleaning the connectors with? Thanks for all your help/ advice its greatly appreciated.
     

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