Limp Mode Frustration

Discussion in 'VW Mk4 Jetta, Golf, New Beetle, Passat TDI forum' started by superdave5599, Mar 3, 2012.

  1. superdave5599

    superdave5599 New Member

    Joined:
    Mar 3, 2012
    Messages:
    4
    Car:
    2002 Golf
    This is a friend's '01 Jetta TDI. Keeps going into limp mode, sometimes with a check engine light, sometimes without. Has been this way for a long time.

    Last spring, I replaced all the vacuum lines while replacing the head gasket, timing belt, and a few other bits in hopes of fixing this. Also replaced the N75 at that time.

    Still goes in limp, and does it more often than not at this point.

    I decided to try some more troubleshooting today. In doing some driving, I found that the ECU would show two different codes after going "limp".

    They were:

    16618 - Boost Pressure Regulation

    P0234 - 35-00 - Limit Exceeded (Overboost Condition)

    16492 - Manifold / Barometric Pressure Sensor (G71) / (F96)

    P0108 - 35-00 - Signal too High


    They were showing up sort of alternatively, maybe a couple times one of them and a couple times the other. Or a couple one, then the other, then back to the one.

    Once, both popped up at the same time.

    I was romping on it going up hills during this testing. It only took a couple seconds of heavy acceleration to cause limp to come up after having shut down the car and clearing the codes.

    I then pulled the MAP sensor from the intercooler. I noted a oily coating on it, so I cleaned it off with air flow sensor cleaner. No change on reinstallation.

    I'm thinking the problem might be the MAP sensor, but my friend doesn't want to throw money at the car hoping something fixes it.

    Any other thoughts?
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  2. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    22,043
    Car:
    2006 Jetta TDI
    Location:
    CT
    That is very possible. Can you swap with known good one? could be rubbing wiring that was disturbed or just worn from age/wear.

    How is VNT actuator function and range? These are most common probs. Also, what was reason for head gasket replacement?
  3. superdave5599

    superdave5599 New Member

    Joined:
    Mar 3, 2012
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    Car:
    2002 Golf
    I have pulled a vacuum on the line from the N75 and felt the rod move.

    To add details from what others have asked:

    The intake manifold was cleaned when I had the head apart.

    I also checked that the rod moved at that time on the turbo.

    Head was off because it was pushing exhaust gasses into the coolant.

    And a couple questions:

    I have heard of people having success blowing the vanes clean by driving it hard. Is this at all effective if it is in limp mode and the turbo is shut down by the computer? Do I need to keep restarting it to clear limp mode (briefly...) or can I keep driving it hard to try to blow it clean even though it is limping?

    Also, if the vanes are stuck from crud, will the actuator rod move? I was under the impression it wouldn't.
  4. superdave5599

    superdave5599 New Member

    Joined:
    Mar 3, 2012
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    Car:
    2002 Golf
    Couple new details:

    I swapped the MAP sensor from my working '02 Golf into the Jetta.

    The Jetta continued to go into limp, and the Golf did not. So I guess this would say the MAP Sensor is ok.

    Also, I compared the feel of the actuator between the two cars. They feel the same to me. I did note that the Jetta's actuator did seem to very slowly lose some vacuum while the Golf didn't, but it was so slow I figured that either 1) it might be a small leak between a hose and the gauge or 2) it was small enough that the computer/N75 could be able to compensate.

    Maybe I'm wrong on that.

    Any other ideas?
  5. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
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    Messages:
    22,043
    Car:
    2006 Jetta TDI
    Location:
    CT
    you'd think it would but a weak spring has same effect, make sure to check what vac press it begins to move at and stop. See the VNT replacement and check article for more details and explanation and checks

    You could have success blowing the vanes that way but the turbo isn't shut down, the vanes are just put wide open. High egt will cook it and burn off crud but since you're not getting high boost you won't get high load and temps. Some have had success using oven cleaner to bake off the crud but it's nasty stuff and will get into the oil.
  6. owen81

    owen81 New Member

    Joined:
    Mar 6, 2012
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    7
    Car:
    2001 Golf TDI
  7. Blackmxz

    Blackmxz New Member

    Joined:
    Mar 9, 2012
    Messages:
    1
    Car:
    2002
    I am working on a 2002 Jetta. The car is going into limp mode also. I tested the N75 valve and the resistance was good. I also tested the Turbo actuator and found it was not working. I tested the old actuator compared to the new and it was bad. After I installed it and I see the actuator move now it still goes into limp mode with the same P0238. It takes about a mile. It runs great until it triggers the code.
  8. owen81

    owen81 New Member

    Joined:
    Mar 6, 2012
    Messages:
    7
    Car:
    2001 Golf TDI
    Have you tried everything in the limp mode fix guide?
    http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm

    It is possible that your sensor is bad as well:

    Originally Posted by Ross-Tech
    16622/P0238/000568 - Manifold Pressure/Boost Sensor (G31): Signal too High
    Possible Symptoms

    * Malfunction Indicator Lamp (MIL) active

    Possible Causes

    * Wiring/Connector(s) from/to Manifold Pressure/Boost Sensor (G31) faulty
    * Manifold Pressure/Boost Sensor (G31) faulty

    Possible Solutions

    * Check Wiring/Connector(s) from/to Manifold Pressure/Boost Sensor (G31)
    * Check Manifold Pressure/Boost Sensor (G31)
  9. pips

    pips New Member

    Joined:
    Mar 10, 2012
    Messages:
    2
    Car:
    VW Golf GT TDi mk 5
    HI,

    I have very little knowledge about car engines. But, I can share with you my experience of my own car (VW Golf GT TDI - Mk 5) and it going into limp mode. similar to yours mine would go into limp mode and the engine light would come on, turning off the engine would reset it but most times the engine light would continue to stay on, it came up with fault codes for overboost, eventually I had the MAF sensor replaced but although this didn't cure is it, it did then come up with another fault code for the throttle body, I had this changed, (expensive!!) and it is now cured!!!!! Yay!!!

    I forgot to mention I took it to another garage before this and then to VW itself and they came up with all sorts of possible cures to do with the actuator the vanes ecu and so on but none of them really knew or could say definatively that it would be cured by doing any of this. Very very frustrating :(

    Happily now though with regard to limp mode it's cured :) now I have another problem with the clutch sticking which I have to flick back up with my foot. ARH!!!

    Dont know if this helps at all!!! Probably not but I checked all these forums before to try to work it all out, I was gratefull for any ideas so decided to share!

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