Speedometer, odometer and trip meter (TC/ABS): Speedometer

Fig 1: Identifying P-Bus Messaging - Speedometer, Odometer And Trip Meter (TC/ABS)

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Identifying Circuit Diagram - P-Bus Messaging - Speedometer, Odometer And Trip Meter (TC/ABS)

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The main instrument unit has an electronic speedometer. The TC/ABS control module receives vehicle speed data from all wheel sensors. The information is processed and transmitted continuously on the P bus. The main instrument unit reads the speed information from the rear left wheel and converts this to km/h.

The information to the TC/ABS from the wheel sensors is in the form of a square wave that varies between B+ and 0 v 29 times per wheel revolution.

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

The speedometer is supplied with current and is controlled by the main instrument unit control module, which also sends information on the speed to the bus.