Driver Information Module (Dim) (2008): Function: Speedometer
The speedometer displays the actual speed the car is traveling at.
Information about speed comes from the speed sensor which is connected to the brake control module (BCM) (4/16) and the transmission control module (TCM) (4/28). The brake control module (BCM) and the transmission control module (TCM) calculate an average speed based on the signals sent from the two front wheels by the speed sensors. The calculated speed signals are then sent to the central electronic module (CEM) (4/56) from the brake control module (BCM) and the transmission control module (TCM) on the high speed section of the controller area network (CAN). Depending on the quality of the signal, the central electronic module (CEM) uses the signal from the brake control module (BCM) or the transmission control module (TCM). The central electronic module (CEM) then sends this information on to the driver information module (DIM) (5/1) which displays the speed.
Transmission control modules (TCM) are only installed in cars with automatic transmissions. In cars with manual transmissions, the speed signal is sent to the central electronic module (CEM) only by the brake control module (BCM).