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Electronic Speedometer problem ????

Discussion in 'The Garage' started by opfor2, Mar 31, 2003.

  1. opfor2

    opfor2 1/2 ton status

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    Yesterday, the Gauge/idle, 20 amp fuse blew on my 1990 Blazer. After I replaced the fuse, I noticed that the electronic speedometer was pointing at 85 MPH and was now not working. I pulled out the speedometer and I can’t find anything wrong with it or the flex connectors . Does anyone have any ideas as to what I can do ? If the speedo is shot what would be a good replacement ?

    Thanks

    Dan…
     
  2. K5 NUTT

    K5 NUTT 1/2 ton status

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    OPFOR...have anything to do with the army's OPFOR?

    Anyways..just bought a 90 V20 Burb..speedo inop. This will help ya out...you will need a DVOM to take some readings...first...jack up the rear end and chock the front end...put it in drive and take an a/c voltage reading at the back of the vss wires...make sure you are getting a reading...if so...you will need to check this reading at the DRAC to ensure the signal is being recieved at the DRAC...thus confirming a complete circuit...the DRAC's job is to convert the a/c voltage to d/c voltage and buffer it to the right signal output depending on gear ratio and tire circumfrance..

    This is how the DRAC is wired...
    824- Lt Blue- Speedo Output
    821- Ppl/Wht- VSS Input
    822- Lt Grn/Blk- VSS Input
    50- Brn- Ignition Power
    450- Blk/Wht- Gnd
    696- Wht- RWAL OUTPUT
    437- Brn- ECM OUTPUT

    Check for a/c voltage at 821/822
    Check power and ground via 450/50
    Check Ecm signal at 437...should be a varying voltage...if not after two minutes sets a code 24...

    I realize this is a bit much as you blew the gauge fuse...however if this short fried the DRAC its good info to have. I applied ign power from the fuse block to 824 disconnected...by tapping the terminal with ign voltage the speedo needle moved...

    The drac is a white box mounted to a spring steel holder inside the dash just under the radio.

    Hope this helps.

    DW /forums/images/graemlins/usaflag.gif
     
  3. opfor2

    opfor2 1/2 ton status

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    [ QUOTE ]
    OPFOR...have anything to do with the army's OPFOR?/quote]



    Yes !!!

    And thanks for the help.

    Befor the speedo went out sometimes it would bounce around this would be something that the older speedo's would do not an electronic one. Would this bouncing be caused by a bad VSS ?

    Thanks again

    Dan...


    WAR IS NOT THE ANSWER, ONLY THE SOLUTION !!!!
     
  4. opfor2

    opfor2 1/2 ton status

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    "Take an A/C reading at the back of the vss wires"

    Do you take a reading with the wires attached to the VSS or at the VSS it's self w/o the wires ? If I'm not mistaken, the VSS has one of those weather sealed connectors on it.

    Thanks

    Dan...
     

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