Speed Sensors 101

How does a speed sensor work with an instrument cluster?

The vast majority of automotive instrument clusters and speedometers produced currently are electronic, meaning they use a speed sensor to determine the vehicles speed instead of a mechanical linkage(speedometer cable) from the instrument cluster to the transmission as in a mechanical speedometer cluster.  This is true in 2003,2004, 2005, 2006 Chevy, Buick, GM, Cadillac, Isuzu, GMC models and many others.

Typically the speed sensor mounts on the transmission and gets its signal from a toothed gear inside the transmission housing.  The sensor has an electric current running and a magnetic tip that sits very close to the teeth on the gear.  When the gear spins, the teeth pass by the magnetic tip of the sensor causing a spike in the electrical signal which the computer registers over time.  The more spikes in a given time period the higher speed it displays on your speedometer cluster. All signals from all sensors are first sent to the computer which in turn sends a signal to the instrument cluster, gauges or the DIC(driver information center).

Speed sensors rarely fail in the 1999 through 2006 GM Vehicles in which we do instrument cluster repair. It is usually in the instrument cluster or gauge panel.