The speed accuracy of the Azuga device is based on the accuracy of the vehicle’s VSS (vehicle speed sensor) message which comes via OBDII. It is commonly known that the VSS signal is the speed reference that the majority of the automotive electronics rely on to achieve their specific functionality. For example the ECM (Engine Control Module) uses the VSS signal to modify engine functions and initiate specific diagnostic routines. The VSS signal originates from a sensor that measures the vehicle’s transaxle speed or more specifically wheel speed. This process is consistent across all makes and models that comply with the OBDII standard from 1996 to date. The accuracy of this signal is governed by DOT standard regulations, as it is used by the Engine Control Module and instrument cluster to accumulate the vehicle’s internal odometer reading and supply the vehicle speed to the speedometer.


There is generally a great deal of confusion in the field regarding the speed that the speedometer provides versus the actual VSS signal. Note that the VSS signal is the most accurate reflection of the vehicle’s speed. The speed that is displayed on the speedometer is generally greater than the actual VSS signal output. This is mandated by U.S. law, and all OEMs supplying vehicle’s in the U.S. generally display a vehicle speed (on the speedometer) anywhere between 1-3 mph more than the actual VSS.