Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

NEED HELP! where is my vehicle speed sensor............

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Intense Blue, Sep 11, 2002.

  1. Intense Blue

    Intense Blue Registered Member

    Joined:
    Dec 2, 2001
    Posts:
    49
    Likes Received:
    0
    I have a 87 K5 4x4 with 350 fuel injection and 700R4.Ever since i restored my blazer about a year ago my check engine light has been coming on now for awhile and my speedometer has not worked either. I just figured the light was coming on cause my speedometer was not working. So after months of putting it off i scanned for codes and code 24 comes up, VEHICLE SPEED SENSOR.I also checked out my speedometer cable and the cable was broke at the transfer case when i took it off, so i replaced the cable and now the speedometer WORKS..but after a few minutes of driving the engine light comes back on. So i disconnected the battery for awhile (reset computer), drove it again and engine light again came back on, so i scanned for codes and still code 24 (vehicle speed sensor) comes up... does anyone know where this sensor is at?? I have checked my chiltons and haynes manual and they don't tell me anything.I called the GM dealers and one said it is on the tranny and one said it's behind the speedometer. Speedometer is cable driven so i doubt that. Any help would greatly be appreciated. thank you.
     
  2. PetaKane

    PetaKane 1/2 ton status

    Joined:
    Apr 17, 2002
    Posts:
    530
    Likes Received:
    0
    Location:
    Oklahoma City OK
    First thing you need to do is take the front bezel off, the thing that is around the gauges, radio, ac, etc. After that carefully figure out the best way to get to the back of the speedo. There is a plug with 3 wires that goes into the speedo, that is the VSS buffer. If that is not what you are looking for, then I think the other thing would be the sensor itself which I don't know where the heck that thing is.
     
  3. Intense Blue

    Intense Blue Registered Member

    Joined:
    Dec 2, 2001
    Posts:
    49
    Likes Received:
    0
    i did remove bezel cluster and got back to the speedometer and all i have back behind the speedometer is the cable that snaps into it...no 3-wire plug at all....
     
  4. Intense Blue

    Intense Blue Registered Member

    Joined:
    Dec 2, 2001
    Posts:
    49
    Likes Received:
    0
    i would also like to add since i've been sitting here thinking about it, that the engine light seems to come on once i start slowing down and that tranny shifts have been slow almost like it's slipping. Also lately it has been stalling out at stop signs alot more but then starts right back up. Not sure if any of these are related but figurerd i better mention it, hoping someone can help.
     
  5. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    87's didn't have an electronic speedometer. The speedo is mechanically driven and contains a small mirror inside that is driven by the same cable that drives the speedo. There is an LED that shines onto the mirror and an optical sensor that is also pointed at the mirror. Each time the mirror goes around, the LED is reflected into the optical detector, creating a signal that gets converted into an electrical pulse. This electrical pulse is the signal that ends up driving the VSS input on the ECM.

    The LED and optical sensor are contained in a light green plastic module on the speedo itself. There are 3 wires that go into this module. If you remove it, you'll see what looks like 2 LED's at the end that's inside the speedo housing. If I remember right, the signal from there is fed into the VSS buffer, then on to the ECM. Find this module and make sure that it's plugged into the harness correctly.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,979
    Likes Received:
    189
    Location:
    Roy WA
    I concur. If its not plugged into the back of your speedometer, thats your problem. Its a light blue or yellow case (that I've seen) for the VSS buffer. If you pull the gauge cluster out, you'll see it.

    Just to reiterate, the "sensor" is the optical "eye" that is bolted to the back of the speedo (one 7 or 6mm screw I think) and then runs down to the buffer (the buffer is maybe 1.5x3" square or so) from the buffer, if equipped with cruise control, the wires will split off, some to the cruise box near the gas pedal, the others to the ECM. Can't recall, but the VSS *needs* ignition 12V, ground, and then has at least one signal out wire, two with cruise.

    They hardly ever fail, it just sounds like yours isn't hooked up.
     

Share This Page