Vehicle Speed (VSS) Sensor(s) input is used by the EMS to determine vehicle speed. The VSS generates a signal that increases in frequency proportionate to vehicle speed. The EMS has a base frequency stored in memory for a distance of one mile. By comparing the input and stored value the EMS calculates vehicle speed.
VSS types include: photo-optic, permanent magnet generators or Hall Effect technology. The EMS may use other sensors on the vehicle such as ABS wheel speed to validate VSS operation.
VSS information is used to calculate vehicle loads including: torque converter application, cruise control, fuel cutoff/speed governance strategies, instrument panel speedometer and more.
Modified drivetrain components such as final gear sets and/or tires can alter VSS input values to the EMS. Improper signals can alter torque converter clutch (TCC) application, shift points, cruise control operation as well as many other systems relying on vehicle speed input.
Related Symptoms
A faulty speed sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.