Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

Vehicle Speed Sensor (VSS)

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OPERATION



The vehicle speed signal is generated from the vehicle speed sensor. Sentra/Pulsar models use two different type sensors.

Reed Switch Type

See Figure 1



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Fig. Fig. 1: Reed switch operation

Reed switch type sensors are used on early systems, through 1990. Beginning in 1991, the reed switch type sensors are only used with analogue (needle) type instrument clusters.

The reed switch type VSS is part of the speedometer assembly, mounted to the rear of the instrument cluster. The shaft of the reed switch is turned by the speedometer cable connected to the rear of the instrument cluster. The reed switch has a small magnet attached to it which causes the reed switch to close every time the magnet sweeps past the reed switch. The typical reed switch VSS is connected to a regulated 5V direct current supply, resulting in a switching direct current (DC) square-wave output signal. The VSS output signal frequency will be directly proportional to vehicle speed and is carried to the ECM through the wiring harness.

Magnetic Impulse Type

See Figure 2



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Fig. Fig. 2: Magnetic impulse type sensor

Magnetic impulse type VSS sensors are used on digital type instrument clusters, beginning in 1991, and all vehicles beginning in 1993.

These sensors use a two wire sensor, located at the transaxle. The shaft of the VSS is turned by the transaxle output shaft. The shaft is attached to a ferromagnetic toothed wheel, which spins in close proximity to a permanent magnet wrapped with many turns of fine wire. As the magnetic field is distorted by the passing teeth of the ferromagnetic wheel, the movement induces a voltage into the coil around the magnet. The voltage produced by the coil will be alternating (AC), and the frequency will be proportional to the RPM of the shaft.

TESTING



Reed Switch Type

See Figures 3, 4 and 5



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Fig. Fig. 3: Reed switch type VSS testing-1987-90 Sentra



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Fig. Fig. 4: Reed switch type VSS testing-1987-90 Pulsar

  1. Check the speedometer operation.

    If the speedometer is not functioning, check speedometer cable and begin with speedometer assembly testing. Repair or replace necessary components.
     
    If the speedometer is functioning properly, proceed to the next step.
     

  2.  
  3. Remove the instrument cluster from the vehicle.
  4.  
  5. Connect a continuity tester across the VSS connector terminals.
  6.  
  7. Turn the VSS pinion gear by hand.
  8.  
  9. As the VSS shaft is turned, the continuity tester should alternate between open and shorted.
  10.  
  11. If the VSS does not switch back and forth between open and shorted as the VSS shaft is turned, replace the VSS.
  12.  

Magnetic Impulse Type

See Figure 2

  1. Remove the Vehicle Speed Sensor (VSS).
  2.  
  3. Connect a voltmeter across the VSS terminals.
  4.  
  5. Set the voltmeter to read low range alternating current.
  6.  
  7. Spin the VSS pinion gear fast and measure the voltage.
  8.  
  9. Voltage should be about 0.5V AC with the VSS spinning.

    If there is no output from the VSS when spun, replace the VSS.
     
    If the VSS tests okay, check wiring to the instrument cluster and from cluster to the ECM.
     

  10.  

REMOVAL & INSTALLATION



Reed Switch Type

The instrument panel mounted VSS is integral part of the vehicle speed sensor. Refer to Chassis Electrical for Speedometer Head removal and installation information.

Magnetic Impulse Type
  1. Locate the VSS at the transaxle housing.
  2.  
  3. If equipped with speedometer cable, disconnect the cable from the sensor.
  4.  
  5. Disconnect the wire harness connector at the VSS.
  6.  
  7. Remove the hardware which secures the VSS to the transaxle. Once the hardware is removed, lift the VSS out of transaxle hole.
  8.  

To install:
  1. Carefully lower the VSS into its mounting hole in the transaxle. Do not force the piece. Allow it the mesh with the transaxle gears.
  2.  
  3. Secure the VSS with the attaching hardware.
  4.  
  5. If removed, connect the speedometer cable.
  6.  
  7. Connect the wiring harness connector to the VSS.
  8.  



Click image to see an enlarged view

Fig. Fig. 5: Reed switch type VSS testing-1991-92 models with needle type gauges

 
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