Circuit Operation

The Vehicle Speed Sensor, mounted to the Transmission, produces an AC signal in the form of a sine wave. The frequency of this sine wave is proportional to the speed at which the Transmission rotates. The speed at which the Transmission rotates is proportional to the speed of the vehicle.

The AC signal produced by the Vehicle Speed Sensor is amplified and converted to a square wave by the Engine Control Module (ECM)/Powertrain Control Module (PCM). The square wave signal is supplied to the Central Control Module (CCM), Cruise Control Module, Radio Control Head and Selective Ride Control Module (Automatic Transmission only).

The CCM uses the square wave signal to display the speedometer and odometer. The Radio Control Head uses this signal to increase the Radio volume as vehicle speed increases. The Cruise Control Module uses this signal for speed regulation.

The ECM/PCM produces the square wave by opening and closing internal solid state switches to ground.

The square wave is at a rate of 4000 pulses per mile. The CCM, Cruise Control Module, Selective Ride Control Module (Automatic Transmission only) and Radio internally convert the number of pulses per mile to determine vehicle speed.