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Thread: New car with Speedo bouncing all over the place

  1. #1
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    New car with Speedo bouncing all over the place

    I just bought this 2005 Corvette and drove it home 700 miles. During the trip The speedo would become very erratic at times which in turn was causing the transmission to shift very erratic. It seemed to be the worst after just stopping to get gas or get something to eat. It would sometimes but not always become stable after 60+ miles of driving but sometimes it would never get any better and drive me crazy until the next fill up. The car was tuned with HP Tuners and I have all the software and licensing and have since made a backup copy of the current tune in case I start making changes I can always restore it from disk. Is there any possibility that there's some setting under HP Tuners in the Speedometer section that could be causing this to happen or is my VSS in the differential just going bad? I do have a receipt showing that the VSS was replaced a few years ago. I'm new to HP Tuners but I work on computers for a living so with some help I can figure it out. Thanks for any help.

  2. #2
    Tuner Rhino's Avatar
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    I wouldn't automatically assume the erratic shifting is caused by what you're seeing on the gauge. The shifting issues could possibly be caused by errors in the tune. Have you tried logging vehicle speed? If so, does it have any inconsistency to what's displayed on the gauges? If you scan the car for DTC's, you should see something if the VSS signal is erratic.

    In both cases, everything you'll need is found in the VCM Scanner. Insert the needed PID's into the table display, connect your hardware to the diagnostic port. With the key forward connect to the PCM then click "start scan"

    For reading the DTC's, click on the toolbar button that resembles the check engine light.

    When I purchased my Avalanche it exhibited similar behavior (minus odd shifting) that turned out to be a bad stepper motor in the gauge cluster. A few dollars and hours later the speedo works great.

  3. #3
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    Quote Originally Posted by Rhino View Post
    I wouldn't automatically assume the erratic shifting is caused by what you're seeing on the gauge. The shifting issues could possibly be caused by errors in the tune. Have you tried logging vehicle speed? If so, does it have any inconsistency to what's displayed on the gauges? If you scan the car for DTC's, you should see something if the VSS signal is erratic.

    In both cases, everything you'll need is found in the VCM Scanner. Insert the needed PID's into the table display, connect your hardware to the diagnostic port. With the key forward connect to the PCM then click "start scan"

    For reading the DTC's, click on the toolbar button that resembles the check engine light.

    When I purchased my Avalanche it exhibited similar behavior (minus odd shifting) that turned out to be a bad stepper motor in the gauge cluster. A few dollars and hours later the speedo works great.
    After driving the car home 700 miles I was able to see a pattern that whenever the speedo was erratic the trans would start acting up with erratic shifting, unlocking the converter, sometimes it would feel like it slipped into neutral for half a second and the RPM's would jump 700-800 RPM's before the trans would grab high gear again and this is all at a steady speed. When the speedo was smooth with no erratic behavior the car shifted perfect. I checked the DTC's over the weekend and the only one I have is for the fuel gauge which just stopped working a few days before I picked up the car. I've checked the speed on the DIC and the in-dash Pioneer Navi system and they all read the same as the speedo so they must all use the same source for getting their information. Is logging vehicle speed done with the HP Tuners software? Is it a pretty simple step? Thanks for any help.

  4. #4
    Advanced Tuner umrjmac's Avatar
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    Quote Originally Posted by NitrousMan View Post
    I've checked the speed on the DIC and the in-dash Pioneer Navi system and they all read the same as the speedo so they must all use the same source for getting their information.
    The navigation system should be using GPS to get both location and speed, so that should independent of the speed sensors in the car

    Quote Originally Posted by NitrousMan View Post
    Is logging vehicle speed done with the HP Tuners software? Is it a pretty simple step? Thanks for any help.
    Logging of vehicle speed is there...in fact its part of the default logging configuration, so you shouldn't need to do anything special to log it.
    Kenne Bell Supercharged 2003 Corvette Z06

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    Quote Originally Posted by umrjmac View Post
    The navigation system should be using GPS to get both location and speed, so that should independent of the speed sensors in the car



    Logging of vehicle speed is there...in fact its part of the default logging configuration, so you shouldn't need to do anything special to log it.
    That's what I was thinking about the GPS but it also shows a G-Force meter which I why I was thinking it was tied into the cars system and plus the Navi system's speedo was jumping around like the cars speedo which wouldn't make sense if it was using the GPS for speed.

    I'll try logging the vehicle speed tonight when I get home. If it's just as erratic as what I'm seeing on the cars speedo is that telling me it's something with the tune or the VSS in the differential? Thanks again.

  6. #6
    Tuner Rhino's Avatar
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    Also, be sure to check your Diagnostic Trouble Codes. If the VSS signal is erratic, I would imagine you may see a history of one of the following codes. (P0500, P0502 or P0503)

  7. #7
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    Quote Originally Posted by Rhino View Post
    Also, be sure to check your Diagnostic Trouble Codes. If the VSS signal is erratic, I would imagine you may see a history of one of the following codes. (P0500, P0502 or P0503)
    The only code I saw in the history was for the dead fuel gauge but I'll double check it tonight. Thanks.

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    So I drove around with HP Tuners running on my laptop and while scanning I was seeing the speedo in the software responding exactly how the speedo in the car was acting. I also noticed that whenever I was totally off the gas rolling at any speed the speedo was perfect but as soon as I touched the gas it would start going crazy. I recorded the data while driving but where do I go from here? Thanks.

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    Tuner Rhino's Avatar
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    From what you're saying I would start with the VSS and it's wiring.
    You mentioned an aftermarket nav/head unit. I would start with disconnecting it from the VSS circuit and insuring the wires are in good condition there. First pull the radio fuse and go for a drive. If the issue disappears the Pioneer is somehow interfering with the signal. If that doesn't help I would look at where it's spliced into the VSS circuit. If it's a bad splice, or one of the cheap "tap" connectors, it's possible that the wire has a break in it or simply grounding out.

  10. #10
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    Quote Originally Posted by Rhino View Post
    From what you're saying I would start with the VSS and it's wiring.
    You mentioned an aftermarket nav/head unit. I would start with disconnecting it from the VSS circuit and insuring the wires are in good condition there. First pull the radio fuse and go for a drive. If the issue disappears the Pioneer is somehow interfering with the signal. If that doesn't help I would look at where it's spliced into the VSS circuit. If it's a bad splice, or one of the cheap "tap" connectors, it's possible that the wire has a break in it or simply grounding out.
    I ordered the VSS so I'll pick it up today and install it tonight. I checked the connector at the Differential and it looked ok so I'll try and follow the wire up the chassis as far as I can to make sure it's not rubbing on anything. It does have a plastic cover protecting the wire around the Diff. I'll check with the Pioneer Navi manual to see where it ties into the VSS and see if I can locate that connection to make sure it's done right. Is there anyway to test the VSS before I replace it? Thanks.

  11. #11
    Tuner Rhino's Avatar
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    If I recall correctly, the VSS is a hall effect sensor. It will be sending a square wave signal who's frequency will increase with speed. The only way I know to test it would be to with an oscilloscope while rotating the driveline. Theoretically you would be able to do it with a DVOM as an AC voltage.

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    That was it, the VSS was the problem. I replaced it tonight and the speedo is perfect and the car runs perfect. Thanks for all the help.