Neon, 2000-2005

Vehicle Speed Sensor

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Operation



The PCM requires the VSS to be able to control the following programs:



Speed Control
 
IAC motor (during deceleration)
 
Injection pulse width (during deceleration)
 
OBD II diagnostics
 
PCM mileage EEPROM
 
Road speed shutdown
 
Speedometer/Odometer (bused message)
 


NOTE
Road Speed Shutdown is the PCM shutting oft fuel injectors above a preset vehicle speed.



Click image to see an enlarged view

Fig.

The vehicle speed sensor on 3-speed automatic and manual transaxle vehicles is a Hall-effect sensor. This sensor is mechanically driven by a pinion gear that is in mesh with the right axle drive shaft. The hall-effect sensor switches a 5-volt signal sent from the PCM from a ground to an open circuit.

Like all Hall-effect sensors, the electronics of the sensor needs a power source. This power source is provided by the PCM. It is the same 8-volt power supply that is used by the CKP and CMP sensors.

The vehicle speed sensor generates 8 pulses per sensor revolution. This signal, in conjunction with a closed throttle signal from the throttle position sensor, indicates a closed throttle deceleration to the PCM. Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value.

When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received). Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed

Removal & Installation



  1. Raise vehicle on hoist.
  2.  
  3. Disconnect the speed sensor connector.
  4.  
  5. Clean area around speed sensor before removing.
  6.  
  7. Remove speed sensor retaining bolt.
  8.  
  9. Remove speed sensor from transaxle, carefully so that sensor drive gear does not fall into transaxle. Should sensor drive gear fall into the transaxle during sensor removal, drive gear must be reattached to sensor.
  10.  
  11. Remove speed sensor drive gear from speed sensor.
  12.  

To Install:

  1. Install pinion gear to speed sensor.
  2.  
  3. Using a NEW O-ring, install the speed sensor to the transaxle.
  4.  
  5. Install the bolt and torque to 7 Nm (60 inch lbs.).
  6.  
  7. Connect speed sensor connector.
  8.  
  9. Lower vehicle and road test to verify proper speedometer operation.

    Click image to see an enlarged view

    Fig.

  10.  

 
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