ISUZU Amigo/Pick-ups/Rodeo/Trooper 1981-1996

Vehicle Speed Sensor (VSS)

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OPERATION



The Vehicle Speed Sensor (VSS) is mounted behind the speedometer in the instrument cluster or on the transmission/speedometer drive gear. It provides electrical pulses to the ECM from the speedometer head. The pulses indicate the road speed. The ECM uses this information to operate the IAC, canister purge, and TCC.

Some vehicles use a sensor located in the transmission. 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



Except Transmission Mounted Sensor

See Figures 1 and 2



Click image to see an enlarged view

Fig. Fig. 1: VSS terminal identification on LS models



Click image to see an enlarged view

Fig. Fig. 2: VSS terminal identification-except LS models


WARNING
If equipped with an air bag system, disarm the system before removing the cluster. Refer to Chassis Electrical for more information.

  1. Remove the instrument cluster assembly.
  2.  
  3. Connect the leads of an ohmmeter across terminals 1 and 2 at the rear face of the cluster.
  4.  
  5. Turn the inner shaft slowly and check that the ohmmeter indicates continuity and an open circuit condition alternately.
  6.  
  7. Replace the speedometer assembly if necessary.
  8.  

Transmission Mounted Sensor
  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.  

REMOVAL & INSTALLATION



Except Transmission Mounted Sensor

On these models, the speedometer must be replaced if the sensor is found to be faulty. Refer to Chassis Electrical for procedures.

Transmission Mounted Sensor

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: Removing the transmission mounted VSS

  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.  

 
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