GM Full-Size Trucks 1988-1998 Repair Information

Vehicle Speed Sensor (VSS)

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OPERATION



The vehicle speed sensor is made up of a coil mounted on the transmission and a tooth rotor mounted to the output shaft of the transmission. As each tooth nears the coil, the coil produces an AC voltage pulse. As the vehicle speed increases the number of voltage pulses per second increases.

TESTING



See Figure 1

  1. To test the VSS, 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 stable.
  4.  
  5. Start the vehicle and place it in gear.
  6.  
  7. Verify that the VSS voltage increases as the drive shaft speed increases.
  8.  
  9. If the VSS voltage is not as specified the VSS may be faulty.
  10.  



Click image to see an enlarged view

Fig. Fig. 1: Vehicle Speed Sensor (VSS) and vehicle speed signal buffer wiring diagram

REMOVAL & INSTALLATION



See Figure 2

  1. Disconnect the negative battery cable.
  2.  
  3. Disengage the electrical connection.
  4.  
  5. Unfasten the sensor retainers.
  6.  
  7. Remove the sensor and gasket or O-ring.
  8.  

To install:
  1. Install the sensor with a new gasket or O-ring.
  2.  
  3. Fasten the sensor retainers.
  4.  
  5. Engage the electrical connections.
  6.  
  7. Connect the negative battery cable.
  8.  



Click image to see an enlarged view

Fig. Fig. 2: Vehicle Speed Sensor (VSS) location

 
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