Vehicle Speed Sensors
Vehicle Speed Sensors come in several different designs depending on the manufacturer. They are used as sensor input for the ABS and Traction Control vehicle computerized systems. This sensor inputs data to the transmission for shift control, cruise control for desired operation, ABS (anti-lock brakes) only to name a few. Most mount on the transmission or rear axle and send a varying frequency to a meter in the PCM (powertrain control module). In many later model vehicles you will find them located in the ABS module. If you don’t see a VSS signal on your scan tool and don’t see it mounted on the transaxle, it’s probably in the ABS system.
This system uses the signal from the front or all four wheel speed sensors to calculate the vehicle speed. The vehicle speed sensor location is typically the transmission case. Transmission/Transaxle mounted speed sensors are driven by a gear located on the output shaft. This speed sensor gear can be either machined or held in place buy a clip. Either way it must be inspected for damage as this could be an underlying cause of premature driven gear wear. The driven gear is typically made of plastic making it softer than the drive gear. It is located on the end of the vehicle speed sensor.
As the shaft of this sensor spins it generates an on off signal to the vehicles PCM / TCM. In later model vehicles this information is shared between computer systems via multiplexing. Vehicle speed sensors located in the differential use a trigger wheel to generate the pulse signal required by the control modules. These VSS systems use different techniques to achieve the same results.
Diagnosing vehicle speed sensors includes checking the sensor, the wiring, PCM, and well as comparing vehicle speed sensor symptoms if no code is present. The vehicle code should in the P 0500 range. The sensor can be tested with a scanner, multimeter, and specifications. If a code is not present there are several symptoms leading to this sensor.
The speed sensor affects so many different systems it may not be so difficult to figure out. For instance, if the vehicle suffered a transmission shifting condition and a dysfunctional speedometer it may be necessary to check for proper VSS operation.
