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Speedo needle jumping around

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  • #1

    Speedo needle jumping around

    I'm thinking a speed sensor on my wife's 2000 TA WS6 is going bad. The speedo needle has starting jumping around erratically every so often. This morning I was driving 70 and it was diving down to 50 or so and back. When the cruise control is engaged it will start accelerating and decelerating so that leads me to believe it is a sensor and not the gauge. Also, it seems like when this happens at slower speeds the tranny starts shifting funny as well.

    Anyone have this problem or know what sensor might be going bad? Also, where is the sensor located? Is it possible that I might just have a bad connection somewhere?
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  • #2
    The speedometer is driven electrically from the vehicle bus, getting a signal from the Vehicle Speed Sensor, VSS- not a mechanical cable, so the culprit has to be a faulty connection somewhere- I *think* the VSS is driven off the back of the transmission output shaft- I think you are going to have to start chasing wires-

    The cruise uses the same signal, so, again, I am pretty sure that is where the problem is- Good luck! ( I hate electrical stuff, they usually are intermittent, so, when you test it, it tests fine, but will continue to go in and out of continuity )
    2001 Z28 A4 - 160 deg t-stat, 3.42 gears, WS6 sway bars, rear springs and shocks, UMI SFC's, Torque Arm and STB, leather Firebird seats, Borla, SLP Y-pipe and lid, ZO6 cam and springs - 332 RWHP and 346 RWTQ, not bad for 'almost stock' - work in progress
    "Black, the fastest color"

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    • #3
      Well, I got the VSS replaced but it still does it. Anybody have any ideas?

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      • #4
        Just for kicks, what kind of batter voltage do you see with the vehicle running?

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        • #5
          Originally posted by Joe 1320
          Just for kicks, what kind of batter voltage do you see with the vehicle running?
          Don't know. My wife just drove the car back to Alabama today. I'll ask her to bring one of my voltmeters back with her when she returns in about a week. I need it to hook up the trailer wiring anyway.

          Let me give you a little more background. I didn't bother with details at first because I thought maybe this was a common problem with these cars.

          The speedo needle first started jumping around at least 2 or 3 years ago. But it didn't do it often and it was just annoying if it happened to do it when you were on cruise control. It has very gradually gotten worse until now I feel like I need to fix it.

          My first thought would be a bad connection and maybe that is the problem. The car has 92k miles on it but has been garaged almost the whole time and has virtually no corrosion anywhere. We haven't been having any other electrical problems. The car runs and drives perfect.

          I'm not sure, but it seems like the problem has lessened since the VSS was replaced (maybe it's just my imagination). But it definitely still does it. I had a shop replace the VSS because I'm away from home living in a hotel room (with no tools, obviously).

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