GM Astro/Safari 1985-1996 Repair Guide

Vehicle Speed Sensor (VSS)

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OPERATION



The vehicle speed sensor is sometimes located behind the speedometer or more commonly on the transmission. It sends a pulsing voltage signal to the ECM, which the ECM converts to vehicle speed. This sensor mainly controls the operation of the Torque Convertor Clutch (TCC) system, shift light and cruise control.

TESTING



  1. Backprobe the VSS terminals with a high impedance voltmeter (set at the AC voltage scale).
  2.  
  3. Safely raise and support the entire vehicle using jackstands. Make absolutely sure the vehicle is secure.
  4.  
  5. Start the vehicle and place it in gear.
  6.  
  7. Verify that the VSS voltage increases as the speed increases.
  8.  
  9. If the VSS voltage is not as specified the VSS may be faulty.
  10.  

REMOVAL & INSTALLATION



  1. Raise and safely support the vehicle.
  2.  
  3. Unplug the electrical connector.
  4.  
  5. Remove the sensor from the transmission or transfer case.
  6.  
  7. Installation is the reverse of removal.
  8.  

 
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