Speedometer with odometer and tripmeter: Speedometer

Fig 1: Speedometer With Odometer And Tripmeter Communication Flow

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Speedometer With Odometer And Tripmeter - Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The main instrument unit is fitted with an electronic speedometer. The ABS control module receives speed information from the left rear wheel sensor. The information is processed and sent continuously to the main instrument connection pin 3.

The information in the form of a square wave pulse varies periodically between B+ and 0 V. This takes place 29 times per wheel revolution.

With the wheels stationary, the voltage may be either B+ or 0 V.

The main instrument unit uses the frequency to calculate the vehicle speed.

The speedometer is controlled by a stepper motor which is pulse-controlled by the main instrument control module. The main instrument unit also emits information on the speed to the bus.