Transmission codes p0731/p0720.... enda could you help?

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  1. Transmission codes p0731/p0720.... enda could you help? 
    #1
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    Tom Beavis's Car Details
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    Hello all, new here and I wondered if I can get any help with these codes. I heard enda maybe the person to ask for help?

    p0731 - Gear monitoring signal implausible, sporadic fault that is currently present
    p0720 - stall speed signal implausible currently not present

    I originally posted this but have since got theses codes above.......

    "Hi Guys,

    First post here! Just had a look around and there is sooo much info you have here, looks really good.....
    Anyway, I've just bought a 2001 330ci Auto. Lovely car and the dealer seems very genuine. On the test drive I noticed a slight knock/clunk from the the rear on hard acceleration, the dealer also noticed it so had it in the garage and did all the diff bushes. Unfortunately that did not really cure the problem (although they did need doing). The garage just suspected the diff was worn and had some slack (100k on the clock), I however bought the car anyway with 3 months guarantee.

    I love the car, aside from its horrendous fuel consumption it drives like a dream. However today problems seemed to have escalated. I don't drive the car hard today I got the usual clunk from a standing start but it also felt like there was a slipping in the transmission, however that could have just been slack in the diff, I really couldn't tell. Anyway the actual problem was the transmission went into limp mode.

    Now I have no experience of BMWs but I am technically minded. There feels like no real problems with the transmission, so all I can think of is that the worn diff could be causing the transmission to go into limp mode? I'm not sure if this is a possibility or indeed if I am on the right lines of diff wear/slack.

    Before I go back to the dealer who is a long distance away I was planning on having my mate who is in the RAC read the fault codes. Would he be able to read the transmission codes or do I need to go to BMW direct?

    I do hope the problem isn't too big even though I have it under guarantee I don't want it to be in the garage for ages as I only got it a week ago. Any advice would be much appreciated.
    Cheers


    Tom"


    330ci Diff / Transmission problems
    Last edited by Tom Beavis; 19-10-2012 at 10:22.
     
     

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    #2
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    TheEnd's Car Details
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    There's a couple of possibilities here, and I have a feeling it'll be the worst one.

    It looks like the torque converter is slipping, which is causing two effects, one is the gear detection/monitoring where it selects a gear, say for example 3rd, and looks at the input speed and output speed, and checks to see if they match knowing the ratio between them.
    If the converter is slipping, the engine rpm is higher and the output speed is lower, making it look more like it's in 2nd, or somewhere inbetween.

    The other code also relates to this, as the stall speed is the rpm at which the torque converter starts to go "solid". Inside is a stator, a large rotor that moves the oil about.
    At low speeds, it turns by itself without really doing anything so the engine can idle in gear with only a mild creep forwards.
    As the engine RPMs increase, it pumps more oil about and it starts to stiffen up and transmit more power through to the gearbox. The stall speed error would be pointing to the converter not putting power through at the engine RPM expected.

    I think what you have is a weak torque converter.
     
     

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    payno (17-10-2012)

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    #3
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    Tom Beavis's Car Details
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    Thanks for that really quick reply! I can see how that relates to my symptoms now actually. I mean under hard acceleration there does feel like some kind of slip going on. Real shame though as I guess it will write the car off. I will take it back to the dealer any how and see what he wants to do. Is this a common thing on auto boxes of this age/mileage? Also any thoughts as to why at say 30mph when you floor it everything is fine and it only happens from a standing start? I mean the RPMs are high at this point and no slippage.....
     
     

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    #4
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    It is possible that if the engine can be driven gently to higher engine speeds, for example 1500rpm+ if will be pumping enough oil to cope with anything, but max power/torque at 1000rpm is too much torque for the locking effect at that speed.

    There is a torque converter seal which can go, bleed the fluid out and reduce the effectiveness, and although I didn't see any 330i torque converters on ebay in a quick glance (there could still be some) they are looking to be about £100-£200 with a similar task to changing a clutch to swap them.
     
     

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    Tom Beavis (17-10-2012)

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    #5
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    Model of Car:
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    I totally see what your'e saying but I just went out for a quick spin and drove it hard, and anything other than a standing start was fine, i.e it pulled like a train through all the gears throughout the rev range even on the red line. It is literally just off the mark, even if you are at walking pace and floor it there is no problem. Would you say I could do anything else to be 99% sure or would just dropping the gearbox be the only solution?
    Last edited by Tom Beavis; 19-10-2012 at 10:20.
     
     

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