Saturn Coupes/Sedans/Wagons 1991-1998 Repair Guide

Vehicle Speed Sensor (VSS)

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OPERATION



The VSS is a permanent magnet variable reluctance sensor, which is mounted in the differential housing of the transaxle. It detects the rotation of the differential assembly and, when vehicle speed reaches 3 mph (5 kph), transmits 16 pulses per revolution to the Powertrain Control Module (PCM). The PCM uses the vehicle speed signal from the VSS to calculate air/fuel delivery and ignition functions. Through a different circuit in the PCM, the VSS is also used to drive the speedometer.

TESTING



See Figure 1

A trouble code will be set if engine speed is above idle, the vehicle is in gear, the MAP sensor output is less than 0.5 volts, and the VSS signal is less than 1 mph (1.6 kph).

  1. If the speedometer is faulty, but there is no diagnostic code set, the problem is most likely in the instrument cluster.
  2.  
  3. If a code is set, unplug the VSS connector and connect an ohmmeter to the sensor terminals. The sensor resistance should be 700-900 ohms.
  4.  
  5. Check the continuity of the wiring between the sensor and the PCM.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Schematic for the vehicle speed sensor circuit

REMOVAL & INSTALLATION



See Figure 2

  1. As an added safety precaution, you may wish to disable the air bag(s), if equipped. refer to Chassis Electrical for the disabling procedure.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise the front of the vehicle and support it safely using jackstands.
  6.  
  7. Unplug the electrical connector from the sensor.
  8.  
  9. Unscrew and remove the sensor from the transaxle housing.
  10.  

To install:
  1. Install the VSS to the transaxle.
  2.  
  3. Attach the sensor electrical connector.
  4.  
  5. Lower the vehicle and connect the negative battery cable.
  6.  
  7. If necessary, enable the air bag(s). refer to Chassis Electrical .
  8.  



Click image to see an enlarged view

Fig. Fig. 2: Vehicle speed sensor installation-manual transaxle

 
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