1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Pedal Value Sensor and MAF - solved

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by SteveX, Dec 7, 2012.

  1. SteveX

    SteveX Senior Member

    Messages:
    1,512
    Likes Received:
    17
    Joined:
    Oct 27, 2009
    Hi Guys,

    Thought I would put a quick post up about my troubleshooting experience with regards to an issue I had in hope that it may prove useful to someone else in the future who searches on the forum:

    My fault happened to be the pedal value sensor, I replaced it and all is now good.



    So, my list of symptoms and experience with this problem:

    - Car drives fine unless you depress throttle to WOT for a few seconds

    - Accelerator responds fine unless the above OR you stamp the throttle fully to the floor and let off (simulating a kick down situation in neutral, but letting off so you do not rev the balls off of the car)

    - Throttle will only respond once error occurs by holding it down for several seconds and then it is a sluggish / very poor response at best

    - If this occurs while driving, you have hardly any acceleration at all and can struggle to get any response when trying to pull away at a junction (several seconds lag)

    - Turn off and back on cures problem straight away

    - Fault does not tally with kick-down being pressed (you can click the kick down with your hand if you like then press accelerator and it's fine only until you put it all the way to the floor)

    - Will do it whether the car is cold or warm (again way to test is quickly stamp your foot fully and let off in neutral, the car will not get chance to rev up and will not damage the engine)



    A few more observations and important points. I originally mistook this fault for a faulty MAF. Reason being, the car only did it when I was cruising and went to overtake on a duel carriageway, then I had severe lack of power and throttle response - assumed car was going into limp mode, although no CEL or warning on dash.

    Volt checking the Bosch MAF is unreliable, I did this and there was some spiking but after replacing even the brand new functioning Bosch MAF did this and gave the same results DON'T RELY on simply checking the voltage (unless I guess it is totally burnt out and doesn't give an output at all).

    After hastily changing the MAF I discovered the fault was not to do with being at speed - taking more time would have showed this, it had nothing to do with the power output of the engine nor the gearbox, nor the temperature of the car, as it could be done in neutral simply by stamping the accelerator fully and quickly to the floor.

    A key point here is the car WOULD rev above 3k RPM, indicating it wasn't in limp mode, however, when moving you would not know this as power and throttle response is so down the car would barely make 3k rpm. On further testing after discovering it was not the MAF given the accelerator pedal was depressed long enough at low speed the car would accelerate beyond 3k rpm.

    The two voltage circuits and the 5v feed to the pedal value sensor were perfect when testing and actuating from the engine bay, they gave the recommended readings specified in WIS so again you can't go on this (unless the signal totally dies). I assume in this case the fault must have occurred when the pedal was quickly depressed, the potentiometer doesn't send the correct output but then the signal recovers. For some reason once the error occurs, even though the two output circuits show the correct voltage after the error, the ECU doesn't seem to recover until a restart.

    Pedal Value Sensor in my case DID show on a code read.

    PVS was my second suspect, and I could have saved the code read money, but in hindsight it was good to get it done to check the car was otherwise healthy and to help pinpoint the issue. There are possibly other things that can sound like this issue, although if your issue ticks all of these boxes then it is highly likely it could be the PVS.

    I have heard however that not all TPS or PVS issues are logged as a code.

    I hope this is of use to someone.

    If anyone requires pin outs or information on reading voltages on the MAF or PVS on the W208 please let me know.


    Thanks,
     
  2. JimM

    JimM Senior Member

    Messages:
    309
    Likes Received:
    0
    Joined:
    Feb 26, 2012
    Location:
    Berks, UK
    Your Mercedes:
    W210 E320 CDi Avantgarde Estate 2002
    You know, the more I read about problems on these cars, and considering the limp-mode problems on my own car, and grounding out the sump on a mere speed bump, and difficult access to work on parts of the car, my old 280E and 300SEL were absolutely the best cars Mercedes ever made and ever will make, and will remain the only-ever Mercedes icons.

    These modern American Chrysler-Merc "Disposables" are just... hair-tearingly Sad!

    Just my Humble Opinion. I never had so many problems on one car ever before. Especially one that had a full Mercedes Service History, and an unused cigar lighter too!
     
    Last edited: Mar 4, 2013
  3. Cicero

    Cicero New Member

    Messages:
    5
    Likes Received:
    0
    Joined:
    Dec 8, 2010
    Location:
    Banbury
    Your Mercedes:
    2004 ML270 Auto
    Thanks to all respondents

    Read all the remarks. The fault has been traced to a problem in the gear box electronics. Checked all your thoughts, split hoses, kick down not engaging etc,without finding problems. A local garage found a fault code, I will advise number, which I didn,t ask for, when fixed. It has gone to a well renowned Gearbox specialist near Birmingham for further checks. Apparently he can check oil pressures etc in the system and he thinks the electronic problem may be accessible without removing the box - hope so. Will update with result and cost later.
    Thanks to you all for a great response.
     
  4. OP
    SteveX

    SteveX Senior Member

    Messages:
    1,512
    Likes Received:
    17
    Joined:
    Oct 27, 2009
    Good stuff, glad you are getting somewhere and hope you get it resolved soon without too much hassle.
     

Share This Page