Question about 1991 Chevrolet S-10 Blazer

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Electronic analog style speedometer not working

91 Chev. S10/T10 Automatic 4WD - Electronic Speedometer was intermittently not working, now it's not working at all. Because I couldn't find a speedometer cable at all, I took the instrument cluster out, and took it to a specialty shop to have the speedometer repaired, I now know the expensive way to find out that it was not the Speedometer in the instrument cluster. According to some internet sights, there are 3 other thinks to check for, 1) fuse 2) VSS 3) DRAC. Checked fuese with light probe, they seem to be find. I cannot located the VSS, its suppose to be located on the tailshaft, driver's side, however in lieu of a tailshaft I have a transfer case, and I cannot seem to find any electrical connections to it. Does anyone know for sure where the VSS is for this model & make? And just so that I know, does anyone know where the DRAC is located as well? I have a repair manual but it seems to skip any inforamtion regarding the VSS and the DRAC.

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  • argonforest Jun 26, 2009

    VSS was located on the tailshaft of the Transfer Case, Drivers Side.

    ECM - remove panel that is below Glove box, ECM is located just above it.

    A defective vehicle speed sensor may cause different problems depending on the computer output control functions. A defective vehicle speed sensor (VSS) may cause improper converter clutch lockup, improper cruise control operation, and inaccurate speedometer operation.

    • Prior to VSS diagnosis, the vehicle should be lifted on a hoist so the drive wheels are free to rotate.
    • backprobe the vss output wire and connect the Voltmeter leads from this wire to ground.
    • Select the 20-volt AC scale on the voltmeter.
    • Then start the engine.
    • Place the transaxle in drive and allow the drive wheels to rotate. If the VSS voltage signal is not 0.5 volt, or more, replace the sensor.
    • When the VSS provides the specified voltage signal, backprobe the VSS terminal at the PCM and repeat the voltage signal test with the drive wheels rotating.
    • If 0.5 volt is available at this terminal, the trouble may be in the PCM (powertrain control module).
    • When 0.5 volt is not available at this terminal, turn the ignition switch off and disconnect the wire from the VSS to the PCM.
    • connect the Ohmmeter leads across the wire. the meter should read zero ohm.
    • Repeat the test with the ohmmeter leads connected to the VSS ground terminal and the PCM ground terminal.
    • This wire should also have zero ohm resistance. If the resistance in these wires is more than specified, repair the wires.
    • The condition of a speed sensor can be checked by going through the diagnostic routines for the system.
    • If this test indicates that a sensor is faulty, the sensor should be replaced.
    • Speed sensors can also be checked with an ohmmeter. Most manufacturers list a resistance specification.
    • The resistance of the sensor is measured across the sensor's terminals.
    • The typical range for a good sensor is 800 to 1400 ohms of resistance.

    1991 Chevy S-10 / T-10 Blazer 4WD Automatic

  • argonforest Jun 29, 2009

    99% of the time, the Speedometer doesn't work because the VSS (Variable Speed Sensor) stops working. The VSS on a 2WD is located on the tailshaft of the transmission, drivers side. On a 4WD the VSS is located on the tailshaft of the Transfer Case, drivers side.

    You will need a 1" socket to remove this sensor. All sockets come as either a 6 point or a 12 point, these are the number of angles in which to lock on to its recepticle, for this purpose a 12 point socket is prefered.



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