Cars with TC/ABS

WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.

The TC/ABS control module on cars with Traction Control is connected to the P-bus. The TC/ABS control module sends a wheel speed signal for each of the four wheels but it is only the information from the rear left and front right wheels that is used.

Wheel speed RL: The TC/ABS control module sends bus message "wheel speed rear left xxx km/h", which used by MIU (internally). MIU sends "Vehicle speed" on to the P-bus and I-bus.

Wheel speed FR: The TC/ABS control module sends bus message "wheel speed front right xxx km/h", which is used by Trionic.

Since the main instrument unit is connected to a bus, all control modules connected to the bus are supplied with information on the speed of the left-hand rear wheel and the odometer reading.

The table of sent bus messages shows that MIU sends vehicle speed, which is used by: Trionic, DICE, SID, ACC, Audio and TWICE. MIU also sends the mileage, which is used by SID for the service indicator.

The various systems use the vehicle speed for the following functions:

The engine control module on diesel cars has a separate lead from ABS for the front right wheel speed. Bus information is not used because the engine management system (like Trionic) requires information on the speed of a drive wheel.
The value is used for the cruise control function and to calculate the current gear position.
Trionic has a separate lead from ABS for the front right wheel speed. On cars with Traction Control, Trionic receives wheel speed information via the bus. The bus value is used for security in cruise control, both values must exceed 40 km/h before it can be engaged. The value is also used as a substitute value if the front right wheel speed should be absent.
The DICE uses the value to activate the radiator fans for A/C on, high outdoor temperature and low speed.
The SID uses the value for trip computer functions.
The ACC uses the value for activating recirculation in connection with high outside temperature and low speed.
The Audio system uses the value for increasing the volume at high speeds.
The TWICE uses the value for automatic locking of the doors when driving off (certain markets).