Driver Information Module (1999-2001): Function: Speedometer

The speedometer displays the actual speed the car is traveling at.

Information about the vehicle speed comes from the speed sensor which is connected to the brake control module (BCM) (called the ABS module on cars up to and including model year 2001) and the gearbox control module (TCM) (4/28). The brake control module (BCM) (4/16) and the gearbox control module (TCM) calculate an average speed based on the signals sent from the two front wheels by the speed sensors. The calculated speed signal is then transmitted to the central electronic module (CEM) (4/56) from the brake control module and the gearbox control module on the high speed section of the Control Area Network (CAN). Depending on the quality of the signal, the central electronic module uses the signal from the brake control module or the gearbox control module (TCM). The central electronic module then transmits this data on to the driver information module (DIM) (5/1) where it is displayed.

Only cars with automatic gearbox have a gearbox control module (TCM). In cars with manual transmissions, the speed signal is transmitted to the central electronic module by only the brake control module on the high speed section of the Control Area Network (CAN).