Types of vehicle Speed Sensor:
Vehicle speed sensors are usually either inductive or optical sensors. The most common inductive sensors consist of a rod magnet on top of a magnetic pin that is surrounded by a fixed coil. This sensor is mounted a fixed distance from a ferromagnetic rotor with teeth. As the rotor turns and a tooth comes into the proximity of the rod, the magnetic flux in the coil changes. This change in flux results in a voltage pulse across the coil. The vehicle’s engine control module counts these voltage pulses and computes the vehicle’s speed.
Optical sensors also generate pulses at a frequency corresponding to the rotor rotation, but instead of measuring magnetic flux, the optical sensor measures either reflected light or light allowed to pass through slits. When using an optical sensor the rotor either has light and dark marks for the optical sensor to detect the reflected light using photo sensors, or a series of slits that allows light from an infrared source to pass through and be detected by a phototransistor on the other side.
Common Symptoms of Bad Vehicle Speed Sensor:
Check Engine Light is triggered
Vehicle’s check engine light can be triggered by the PCM for different reasons; one of which is a faulty VSS. The vehicle will need to be connected to an OBD-II scan tool to confirm whether the error code is due to a VSS malfunction. Other warning lights such as those for the ABS and traction control systems may also appear on the dashboard.