Speed Sensor Buffer

The Vehicle Speed Sensor Buffer (DRAC) module processes inputs from the Vehicle Speed Sensor (VSS) and outputs signals to the Speedometer, Engine Control Module (ECM) and the Cruise Control Module.

The VSS is made up of a 40-tooth rotor and a coil mounted on the transmission. As each rotor tooth nears the coil, the coil produces an AC voltage pulse. Each revolution of the rotor produces 40 AC voltage pulses. As the vehicle speed increases, the number of AC voltage pulses per second increases.

The Vehicle Speed Sensor Buffer (DRAC) module takes the voltage pulses from the VSS and uses them to open and close four Solid-State output switches to ground at a rate proportional to vehicle speed.

The Speedometer switch opens and closes at the same rate as the VSS pulses. The ECM and Cruise Control switches open and close at half the rate of the VSS pulses.

The Vehicle Speed Sensor Buffer (DRAC) module is matched to the vehicle based on transmission, final drive ratio and tire size. It is important to ensure that the correct Vehicle Speed Sensor Buffer (DRAC) module is installed in the vehicle if replacement is necessary.