Transmission problems
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  • 2 Post By amunderdog
Cadillac Seville / Cadillac Eldorado Forum Discussion, Transmission problems in Past Cadillac Vehicle Discussion; Well I have posted here once about my car having transmission problems( meaning it wouldn't shift out of first gear) ...
  1. #1
    93 John Eldorado is offline Cadillac Owners Member
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    Transmission problems

    Well I have posted here once about my car having transmission problems( meaning it wouldn't shift out of first gear) and the gentleman at the Cadillac dealership told me it was an input speed sensor problem. Now I recall someone saying that wasn't it if the speedometer was not working, well here is the weird part. I picked my baby up from the dealership and started driving it and it shifted perfectly, even the speedometer was working great. Then about 3 miles and a speed bump later the speedometer stopped working ( but the tach did ) and it went back into first gear and never shifted from there. What the heck could be wrong now??? Please help!!!

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    ronluh is online now Cadillac Owners Member
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    Pull codes and list with definitions..... then we can offer opinion.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Transmission problems

    Two different animals here -

    ISS - transmission Input Speed Sensor - reads input shaft speed - expensively buried inside the transmission with no easy fix

    VSS - Vehicle Speed Sensor - on top of the right axle output shaft housing - 20 minutes on a lift

    Both sensors are powertrain, shift, and vehicle controls; the VSS also sends pulses to operate the speedometer.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Transmission problems

    The early '90's 4T80Es where plagued by broken shift solenoids, enough so that replacement "kits" included a hold down strap to prevent it. If yours are original, maybe they are the problem. They SHOULD set a DTC.

  6. #5
    stoveguyy is offline Cadillac Owners Connoisseur
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    Dealer said it was input speed sensor. So he did no work? I assume you just left and car worked ok for a few miles?

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    amunderdog is offline Cadillac Owners Enthusiast
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    Re: Transmission problems

    If they poked around and it worked, then you hit a bump and it now it does not work.
    I would be going over the wire harnesses very carefully.
    98eldo32v and 98eldo32v like this.

  8. #7
    93 John Eldorado is offline Cadillac Owners Member
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    Re: Transmission problems

    Quote Originally Posted by stoveguyy View Post
    Dealer said it was input speed sensor. So he did no work? I assume you just left and car worked ok for a few miles?
    Yes!! That's just what happened. They told me it would cost me $2600 to fix it and the input speed sensor harness would be $800 alone.

  9. #8
    Aztec ETC ECS's Avatar
    Aztec ETC ECS is offline Cadillac Owners Connoisseur
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    Re: Transmission problems

    Did you pull codes?

    Sounds more like the VSS and only the VSS or wiring thereof. (Outside the trans)
    The trans is capable of shifting without the ISS. It may shift erratically but will shift and should also get a "traction disabled message".

    The ISS would be an expensive repair but I don't believe it's the case here. If you can't fix yourself, take it to an independent shop.

  10. #9
    1BadCadSTS's Avatar
    1BadCadSTS is offline Cadillac Owners Connoisseur
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    Tech 2 should show data sent to the PCM from both ISS and VSS. I would assume they were bein an honest dealer and showed varying information coming from the ISS sensor which is why they recommended its replacement.

  11. #10
    Aztec ETC ECS's Avatar
    Aztec ETC ECS is offline Cadillac Owners Connoisseur
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    Re: Transmission problems

    Quote Originally Posted by 1BadCadSTS View Post
    I would assume they were bein an honest dealer
    Really?
    I thought you would know better than that, Batman.

    I bought a mint cheap STS with a bad ISS and drove it home, 210 miles, some years back. Upshifted pretty good.

    There is a lot of labor to change the ISS, but the part is not $800.
    http://transpartsdirect.com/4t80e-in...1-p-10811.html
    Maybe he misinterpreted what they told him.

  12. #11
    1BadCadSTS's Avatar
    1BadCadSTS is offline Cadillac Owners Connoisseur
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    Yea they are RARE but based on the info provided its still difficult to tell. If the OP is local ill be more than happy to hook it to my snap on modus and take a peak at the systems.

    Based on what he said above the speedo only started to act up once he picked it up but he has had prolonged transmission issues which to me makes it a difficult call.

  13. #12
    Aztec ETC ECS's Avatar
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    Re: Transmission problems

    I still say, other than internal damage, the only thing that would cause no upshift out of first would be the VSS.
    If the ISS was bad, the PCM would see that as the engine at zero RPM's. As soon as the VSS signal increases, it would upshift. Should stack shift, but for whatever reason I've never seen it do that.

  14. #13
    1BadCadSTS's Avatar
    1BadCadSTS is offline Cadillac Owners Connoisseur
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    Best course IMHO would be to do the vss. It's cheap and easy to swap. Problem persists then its either wiring and we test continuity or its the ISS/wiring.

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