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Thread: Engine Management light on ( P0299 )

  1. #1
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    Engine Management light on ( P0299 )

    I have a 2010 mercedes engine Cdi with PDF filter/burn cycle. 42k miles.

    Car has been just suddenly slowing down occasionally for the last month, roughly once a week, requiring me to pull in, switch off, wait a few minutes, start up and away again as normal, til it happens again.

    Then this week the engine management light came on and checking with my code reader, just the one fault code........
    P0299 Supercharger/underboost.

    Can anyone expand on the fault and what it will take to sort it, thanks.

    In the meantime I have reset the code, and engine management light is now off. Car runs fine most of the time, till it suddenly slows down.
    Last edited by colin2x2; 16-11-2017 at 03:47 PM.

  2. #2
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    Modern cars don't blow the exhaust up if you turn the ignition off like they used to so you can just turn the key off and on again while driving but remember your headlights will flash if it is night time.

    Low boost (assuming sensors are OK) is usually easy enough to find, probably a split hose or an extremely blocked air filter can do it though I doubt that is your problem. It could be the EGR that is severely restricting air flow. More investigation is required. Get Torque and monitor the boost while driving, see if it is reasonable.

    PDF Portable document format.
    DPF Diesel particulate filter.


  3. #3
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    I forgot: The 451 wastegate is prone to seizing so it may be that which is stuck open.

  4. #4
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    Quote Originally Posted by Mjolinor View Post
    I forgot: The 451 wastegate is prone to seizing so it may be that which is stuck open.
    It ‘s the 54 diesel , it’ll be emission related sensors failing/failed, not that cheap either.

    The Big guy can sort that out
    You're so money supermarket and you don't even know it!

  5. #5
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    Right, thanks.

    The first and cheapest thing I will try, is change the air filter, as its never been changed since I bought the car four years ago, just due to its hellish location, and i have no idea if the former owner got it changed either. Got a feeling it will be the original filter, so could be in a pretty bad way with regard restricted air flow.

    Just ordered an air filter on Ebay right now. Going to end up with some bleeding fingers trying to change it, and see if this is an easy fix, or not.

    Can you tell me how many clips hold down the air filter cover on the Cdi, as its difficult to see in there?

    Just read this on an older post, No wonder I have been putting it off.....

    "The air filter on the 54hp CDi can be changed by jacking the car up on the passenger side rear and removing the rear wheel. Then remove the wheel arch inner liner and the top of the air box can now be removed through the wheel arch. I would love to give the designer of this a swift kick in the nuts for making an air filter such a pain in the ass to change"
    Last edited by colin2x2; 16-11-2017 at 08:19 PM.

  6. #6
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    That's bolox. I think there are three clips. One either side and easily visible and one underneath the outlet pipe in the middle. Memory is not what it was, I may be making the middle one up, my brain does that, my mind wanders too, where is that kit kat gone. Must get some milk today.

    It is not hard to get it off and replace the element and you don't need any special instructions to do it.

    If you need someone to tell you how to do that then you should be taking it to a garage to be fixed, it really is that ordinary.

    I can't see what "emission related sensors" would lead to a low boost warning. All of those have very specific fault codes of their own and are generally pretty reliable.

  7. #7
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    So what you are saying Mjolinor, is that you can reach in through the engine cover hole, reach in behind the hole as the air filter is way back there in the CDi (unlike the petrol versions, that you can get to easy), and undo the three clips get the cover off the air filter and replace it, and put the cover back on.

    If that is the case, then tha'ts a lot less hastle, thanks.

    Last edited by colin2x2; 17-11-2017 at 03:58 PM.

  8. #8
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    Yes you can.

    3Dy5CPe.jpg

    My filter (Late 2009) is where the black box is. There are three clips on the bottom side (in the drawing. There are no clips in the back, there are small sticky out bits that fit in the lid. You have to remove the air pipe from the lid first then just remove the top off the box.

  9. #9
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    My air filter box is visible in this picture. You can clearly see one of the clips and the pipe you need to undo under my leatherman. I seem to have a clip missing on the right and seem to think there may be one underneath the pipe. It is a conundrum to me why there were 2 of these clips in the drivers door pocket.


  10. #10
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    Thanks for the info.

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