Q: What is the purpose and operation of the Vehicle Speed Sensor (VSS) for Chevrolet C1500 and K1500?
A: A toothed rotor on the transmission output shaft causes the Vehicle Speed Sensor (VSS), which is a permanent magnet generator mounted on the transmission, to produce an AC voltage. The ECM/PCM uses this signal for different engine and transmission control functions as well as driving the speedometer on the instrument panel. Driveability and transmission problems can result from a defective VSS. To check the VSS operation, raise the vehicle and locate the sensor. Check for any looseness or breaks in terminals and wires and repair if necessary. Back probe the two wire terminals of the VSS connector and connect a voltmeter set on AC volts scale. With ignition key ON, engine OFF, rotate one rear tire while monitoring voltmeter. As minimum as 0.5 volts should be produced by the sensor with increasing speed of rotation of transmission output shaft. Turn off ignition key and disconnect electrical connector from sensor. Measure resistance across two terminals using ohmmeter, which should be approximately 1,000 to 3,000 ohms at 68 degrees F.Temperature If test results are incorrect replace VSS.Replacing means raising vehicle, disconnecting electrical connector, removing mounting bolt then drawing VSS from transmission case.Replace sensor O-ring.Then reinstall VSS back following opposite steps used during removal.