2004 E46 316ti - Plausibility diff. pressure sensor(FIXED)

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  1. 2004 E46 316ti - Plausibility diff. pressure sensor(FIXED) 
    #1
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    Hi there,

    I'm starting a new thread about this as my previous one went a little off base so i wanted to get this all down into one area.

    Since i've had the car i've had occasionally starting problems and intermittent cutouts. Basically i turn the key and sometimes it will rev up to 1000 and then down to 300 and die. Sometimes the engine catches itself and brings the revs back up, but sometimes not. You can stop it with some gas. It also occasionally just dies when idling (at a junction for instance, or alternatively you can leave it in the garage ticking over and it will eventually die)

    The fault code for any of these circumstances is (including it stops it from stalling by suddenly catching itself)

    PHP Code:
    2D29  CDKPDDSS Plausibility diffpressure sensor, (FROM INPA)

    Error counter:    1
    Logistic counter
    40

       Mileage                                  65560     km
       Supply voltage 
    (ub)                         13.28  V
       Engine speed 
    (nmot)                        240.00  /min
       Engine temperature 
    (tmot)                   53.25  degrees C
       Ambient pressure 
    (pu)                     1035.00  hPa

       Unknown type of error
       Test conditions fulfilled
       Error present now
    but not yet stored (debouncing phase)
       
    Error would not cause a warning lamp to light up
       Diagnostic active 
    You can reset the code but it will come back when it does it next.

    So far this is what has been done:-

    Indy:- Firstly noted it was a new sensor fitted in March just before i got it. He changed Timing chain guide, smoke tested manifold for leaks (none) has tested the sensor, the wiring and the ecu. All of which come up fine. He told me to take it to BMW as he basically thinks the whole thing is perfect and doesn't see why the code is coming up, he also checked the crank sensor and found it to be ok. The ccv was also checked and found to be in perfect shape.

    BMW Sytner:- Magically found another error about the vvt servomotor and decided the "Plausibility diff. pressure sensor" was an offshoot of that. So i trusted them and they fit a new servomotor at a crazy price. It stalled almost as soon as i got out of the car park. They have done a free diagnosis for me after that and are now saying it "may" be the crank sensor (which checked out ok by the INDY. But i don't see why it would be pulling the pressure sensor code. And after their vvt servomotor episode i don't see any reason to trust them.

    I'm at a massive loss with what to do now. Apart from perhaps finding another bmw indy. Is there anyway a small airleak wouldn't have been picked up in a smoke test? The indy to his credit had the manifold off more than once but couldn't find anything.

    I've already sunk a lot of money into supposed fixes and there doesn't seem to be anyone who could figure this out.

    Any thoughts would be greatly appreciated.

    Jon B
     
     

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  3.  
    #2
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    A quick update on this as i didn't realise there were extra pages on INPA.

    Here is what it is reading for the Manifold Pressure:-



    As you can see the pressure the sensor is reading is 500+ hPA when it seems to be suggesting that the value should be between 45-55 hPA. When INPA is actively scanning the pressure does vary (always 400-500) so the sensor is varying the voltage.

    Assuming the sensor/wiring is ok (it's already been replaced) then it screams vacuum leak but the smoke test didn't find anything.

    I'm gonna take it down to Autotech on Tues and see what they say (having had opinions from other garages who don't seem to know whats going on...
     
     

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    Have you thought of getting the engine system smoke tested again? be worth it to rule out the CCV valve and other items.
     
     

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    JonnyBrad81 (05-06-2011)

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    its a wonder it will run to any acceptable degree in the first place as with it duff it will be confusing the ECU and fuel injection calculations all over the place..

    what does your short term and long term fuel trim values look like in INPA?
    330i sport a big chunk of berlin...

     
     

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    JonnyBrad81 (05-06-2011)

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    Quote Originally Posted by dailydoggy View Post
    its a wonder it will run to any acceptable degree in the first place as with it duff it will be confusing the ECU and fuel injection calculations all over the place..

    what does your short term and long term fuel trim values look like in INPA?
    AFAIK with the crazy reading it gets it just dumps it into limp mode and the ecu uses a default value (say 50 hPA) and uses the backup throttle to control the engine instead of the valvetronic. The same thing happens when you run the sensor unplugged - it runs fine then using a default value. (You get a code telling you its unplugged) I will check the fuel trim readings in Inpa tomo.
     
     

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    Quote Originally Posted by Ronnie View Post
    Have you thought of getting the engine system smoke tested again? be worth it to rule out the CCV valve and other items.
    Yeah i'm taking it to a new Indy (Autotech) on Tuesday armed with this info. The last Indy checked the ccv about 4 weeks ago and felt it was ok. We'll see how it does in someone else's hands. (The BMW dealer in Cardiff was useless - checked the sensor, told me it was ok, cleared the fault then shoved it out the door)

    It's either gotta be a vacuum leak somewhere or the wiring/sensor is giving duff info.
     
     

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    The latest Indy has told me its "probably the engine loom" they have had a similar fault on a mini (uses same sensor) which was finally cleared up after a loom change. Tomorrow i'm going to measure the resistance of the wires to the ECU. However even if it checks out there is no way of telling what is happening when the engine is heating them. I've been told the wiring used is pretty crappy so it doesn't take much for one to have an issue. To replace the loom is 270 for the wiring then whatever labour, or i could do it myself.

    I'll update this post with my findings as i know more than one person has had this issue before.
     
     

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    Finally had a spot of weather so today i checked the wiring.

    All i can say is the resistances are perfect. 0 on all 3. This was done with an engine that had just been driven so the wiring would still be warm.

    I also inspected the breather pipe on top of the manifold and might have made a discovery! I pulled it off and inspected it. It seemed ok. However when i put it back and started the car the pressure readings were actually normal (30-70) so i took it out for a drive. After about 20 minutes with the laptop plugged in and INPA plugged in the pressure suddenly went up to its 500-600 value and the code got stored.

    I then reset the code and started the car again and the pressure was back to 40-50.

    I wonder if this is a red herring or whether the pipe is starting to go and causing air to leak out at some points. I'm going to order one on monday and replace as its only 15 quid.

    I'll keep this page updated.
     
     

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    Ronnie (30-06-2011)

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    Not updated this is a while as have been away. Replaced that pipe (no effect) and have now had a BMW specialist replace the 3 wires that run back to the ECU from the sensor to rule out loom. It still faults.

    The mechanic is now pretty certain its got to be shorting inside the ECU itself. So an ECU replacement is about the only thing we have left to try. Its an expensive thing to do (the n46 ecu's are 700 quid) but there is literally nothing else to try.
     
     

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    You may be able to get a ECU slightly cheaper from our forum vendors Hereford BMW.
     
     

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