Traction Control System
Traction Control Systems (TCS) OverviewSystem Diagram
Twin Throttle System:
General Description
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 tire wear, etc.
The TCS function is not affected if an emergency spare wheel of "Mini-Spare" type is used.
Permissible Wheel Spin
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.
Functions and Components
CONTROL MODULE INPUTS
-ON/OFF switch (pin 1)
-Engine rpm (pin 6)
-Speed signal, FR (pin 7)
-Speed signal, RR (pin 8)
-Diagnostics lead K (pin 9)
-Position signal, main throttle butterfly (pin 11)
-Ground (pin 13)
-Brake light switch (pin 23)
-Speed signal RL (pin 24)
-Speed signal, FL (pin 25)
-Position sensor, TCS throttle butterfly (pin 27)
-Voltage supply from +15 (pin 28)
-Ground (pin 30)
-Voltage supply from +30 (pin 32), also output
CONTROL MODULE OUTPUTS
-Position sensor, TCS throttle butterfly (+) (pin 3)
-Position signal, TCS throttle butterfly (automatic transmission only) (pin 4)
-Disengagement, Cruise Control (pin 5)
-Diagnostics, K lead (pin 9)
-Indicator lamp, TCS/control module or automatic transmission (pin 12)
-TCS throttle actuator motor (+) (pin 18)
-Position sensor, TCS throttle butterfly (-) (pin 20)
-Disconnection, full-load enrichment (pin 21)
-TCS OFF warning lamp (pin 26)
-TCS throttle actuator motor (-) (pin 35), also input
Principal of Operation-Control Module
The 35-pin TCS control module is located under the right-hand front seat which must be removed to provide access to the control module.
When the TCS throttle actuator motor is not supplied with power, the throttle butterfly is held in the open position by a spring.
When the ignition switch is turned to the Drive position, the actuator motor rotates the butterfly towards the wide open position for 128 ms and so ensures that it really is wide open. The actuator motor is then switched off (while the butterfly is still held in the wide open position by the spring) and after a further 128 ms the signal from the butterfly position sensor is stored as "wide open butterfly" in the control module.
As soon as the speed of the car exceeds 4 km/h and engine speed exceeds 600 rpm, the TCS throttle butterfly is synchronized with the regular throttle butterfly.
The first time the accelerator is fully released after starting and engine braking takes place, operation of the TCS butterfly, which closes fully for 128 ms, is checked afresh and its position is stored as "fully closed butterfly" in the control module. With the accelerator still released, the actuator motor will now be switched off for 256 ms and give the butterfly time to open by spring force to an angle of at least 25°.
Following this the TCS throttle butterfly is again synchronized with the regular throttle butterfly.
When the ignition is switched off or if a fault arises in the system, the power supply to the actuator motor is immediately switched off and the throttle butterfly is opened fully by spring force.
In the event of an internal fault in the control module, a diagnostic trouble code is generated, the TCS OFF lamp lights up and the Traction Control System is rendered inoperative.
As a spare part the control module is unprogrammed and must therefore be programmed with the aid of an ISAT in connection with installation. For the Saab 900 the TCS control unit is to be programmed according to whether the car in question is equipped with a manual gearbox or automatic transmission.
Control Module Power Supply
BATTERY VOLTAGE +30
The TCS control module is supplied with battery voltage on pin 32. This voltage is used by the control module to control the throttle actuator motor.
If no +30 voltage is present, the TCS OFF lamp lights up and the system is rendered inoperative. If the +30 supply is interrupted, the control module will still retain any diagnostic trouble codes that are stored in its memory.
BATTERY VOLTAGE +15
With the ignition switch in the Drive position the control module is supplied with +15 voltage on pin 28. This voltage is used to activate the system.
Grounding Points
The ground connections to pins 13 and 30 are joined together internally in the control module and from an electrical viewpoint comprise the same point. Duplication of the grounding points is carried out to improve reliability and safety.
With the ignition switch in the Drive position the control module's grounding points can be checked with a voltmeter by measuring the voltage across pin 13 and the battery's negative terminal and across pin 30 and the battery's positive terminal.
- The voltage should be less than 0.1 V.