Silverado 2008

Vehicle Speed Sensor (VSS)

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Location



Specific to:

Chevrolet Silverado 1500 2008

The Vehicle Speed Sensor (VSS) is located on the tail section of the transmission on 2WD vehicles, except Allison transmission. On 4WD vehicles the sensor it is located on the transfer case, except Allison transmission. On Allison transmission the sensor is located on the transmission assembly.

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Fig. VSS mounting-2WD



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Fig. VSS mounting-4WD



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Fig. VSS mounting-Allison transmission

Operation



Specific to:

Chevrolet Silverado 1500 2008

The Vehicle Speed Sensor (VSS) supplies vehicle speed information to the PCM.

The Vehicle Speed Sensor (VSS) is a permanent magnet output coil device that monitors the vehicle speed. A reluctor is attached to the transmission/transaxle final drive, and is used to generate a constant signal as it passes the VSS magnetic coil. The VSS Sensor utilizes system voltage (12 volts DC), or reference voltage (5 volts DC) to generate a digital output signal to the PCM that is based upon a 0.5 volt AC reference. The alternating magnetic field is used by the sensor output electronics to produce a generated wave form. The VSS waveform is used by the Powertrain Control Module (PCM) to calculate engine and vehicle load, ignition timing, fuel injector timing and pulse width, fuel cut, and the speedometer display.

Removal & Installation



Specific to:

Chevrolet Silverado 1500 2008

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise and support the vehicle safely.
  6.  
  7. Detach the electrical connector from the VSS sensor.
  8.  
  9. Remove the sensor from its mounting.
  10.  
  11. Remove the O-ring seal.

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    Fig. VSS mounting-2WD



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    Fig. VSS mounting-4WD



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    Fig. VSS mounting-Allison transmission

  12.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Installation is the reverse of removal.
  2.  
  3. Coat a new O-ring with transmission fluid.
  4.  
  5. On Allison transmissions install the sensor into the bore. Align the hole in the retaining bracket with the bolt hole in the sensor.
  6.  
  7. Tighten the bolt to 97 inch lbs. (11 Nm) on 2WD or the sensor to 13 ft. lbs. (17 Nm) on 4WD. On Allison transmissions tighten the bolt to 108 inch lbs. (12 Nm).
  8.  

Testing



Specific to:

Chevrolet Silverado 1500 2008


NOTE
Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Connection And Wiring Diagnosis

Specific to:

Chevrolet Silverado 1500 2008

Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Many intermittent open or short circuits may be caused by wiring harness and connector movement due to vibration, engine torque, bumps and rough pavement, etc.

  1. Test the wiring harness and connectors by performing the following tests:

    Move the related connectors and wiring while monitoring the appropriate scan tool data.
     
    Move the related connectors and wiring with the component commanded ON and OFF. Using a suitable the scan tool, observe the component operation.
     
    With the engine running, move the related connectors and wiring while monitoring component operation.
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
     

  2.  
  3. Test the connector terminal pins and/or wiring by performing the following tests:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body.
     
    Inspect for improperly formed or damaged terminals and test for incorrect terminal tension.
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and/or brittle sections of wire in the suspect circuits.
     
    Inspect for wires that are broken inside the insulation by gently pulling on suspect sections of wiring.
     

  4.  

Related Diagnostic Trouble Codes

Specific to:

Chevrolet Silverado 1500 2008



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Fig. Related Diagnostic Trouble Codes

VSS Circuit Testing

Specific to:

Chevrolet Silverado 1500 2008

Use a suitable scan tool or a Graphing Multi-Meter (GMM in order to view the VSS data.

VSS logic is based on alternating lines of magnetic flux which generate an analog signal to the PCM, and are based on the vehicle speed.

Verify that the engine that there is no foreign material obstructing the path between the reluctor and the VSS. If any engine mechanical faults are evident, locate and repair as required before continuing.

A Digital Volt-Ohm Meter (DVOM) may be used to verify the condition of the wiring: additional information may be acquired by taking measurements at the sensor connector as well as the PCM connector. If significant resistance is measured (greater than 5 ohms), check the wiring harness and connections for corrosion, poor pin connections, or damaged wires.

If all engine wiring and pin connections are confirmed, disconnect the VSS to verify the signal with a GMM, and verify PCM communication before replacing the VSS Sensor.

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Fig. VSS Range Chart

VSS Strategy

Specific to:

Chevrolet Silverado 1500 2008

The VSS provides a magnetically generated signal waveform (See Figure 1) to the Powertrain Control Module (PCM) for a number of engine control, drive train, and information display system calculations. The VSS signal frequency varies according to vehicle speed, and is compared with the Crankshaft Position (CKP) Sensor and Camshaft Position (CMP) Sensor signals for measured operating conditions. The magnetic waveform pattern is used by the Powertrain Control Module (PCM) to calculate engine and vehicle load, ignition timing, fuel injector timing and pulse width, and the speedometer display.

 
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