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Description of the TCS forB258

Description of the TCS for B258


The TCS consists of the following components:





• TCS control module

• Throttle body with DC motor and throttle butterfly position sensor

• TCS indicator lamp

• TCS OFF warning lamp

• ON/OFF switch

The Traction Control System (TCS) prevents uncontrolled wheelspin during heavy acceleration and on icy or slippery road surfaces.

The TCS for M94 Saab V6 cars is a new Saab system based on the use of two throttle butterflies. It is also called the Twin-Throttle System (TTS).


This traction control system adjusts engine torque by regulating the throttle butterfly in the extra throttle body which forms part of the system.

This extra TCS throttle body is mounted after the regular cable-operated throttle body. When the car is in motion, the TCS throttle follows the regular throttle under the control of the TCS control module.

As soon as the maximum permissible wheelspin is exceeded, the opening angle of the TCS butterfly is reduced in relation to that of the regular throttle butterfly. This brings about a reduction in engine torque until wheelspin is no longer excessive.

The control module's most important information is obtained from the four wheel sensors via the ABS control module, but the TCS system does not affect the brake system at all. To compensate for normal changes in the circumference of the wheels, the system is adaptive in regard to tyre wear, etc.

The TCS function is not affected if an emergency spare wheel of "Mini-Spare" type is used.


Permissible wheelspin


When starting on a slippery road surface, the Traction Control System permits a certain amount of wheel spin up to a maximum of 3 km/h. This upper limit for permissible wheelspin successively drops to about 1.5 km/h at 35 km/h, which corresponds to a "slip" of about 4.5%%.

Permissible wheelspin then remains constant up to 100 km/h at which speed the "slip", which is the relationship between permissible wheelspin and road speed, will have dropped to 1.5%%.

Permissible wheelspin increases again at speeds above 100 km/h until it reaches about 3.5 km/h at 200 km/h, corresponding to a "slip" of about 1.8%%.

Permissible wheelspin is again constant at speeds above 200 km/h.

Checking throttle butterfly operation


The control module contains a special program for checking the TCS throttle butterfly and synchronizing it with the regular throttle butterfly. The program includes calibration of the butterfly's full throttle (wide open) and idling (fully closed) positions, checking the operation and force of the spring which returns the butterfly to the wide open position, and also checking that the butterfly runs freely without binding.

Further information on control module calibration of the throttle valve position is provided in the "Control module" section.