2005 Saab 9-3 Owner's Manual - Page 171

Starting and driving 169 Traction Control System (TCS) Anti-spin system WARNING When driving normally, the TCS system helps to improve the car's directional stability. The TCS must not be regarded as a system to enable the driver to maintain higher speeds. The same precautions must be adopted as normal for safe cornering and driving on slippery roads. If the two front wheels are rotating at the same speed but are turning faster than the rear wheels, the torque from the engine is reduced to eliminate the difference. The process continues until all the wheels are rotating at the same speed. The advantages of the TCS become most apparent when the cohesion between the front wheels and the road surface is so low that one or both of the wheels would lose their grip were the car not equipped with the TCS, e.g.: • When the car is pulling away or accelerating with the front wheels on different surfaces (e.g. one slippery and one dry), the TCS functions like an electronic differential lock, making sure that both wheels rotate at the same speed. • When the car is pulling away or accelerating on a slippery surface, in which case the system eliminates wheelspin. The system also functions when the car is reversing. • When cornering, if the inside front wheel rotates faster than the other wheels. TCS OFF lights up under the speedometer if: • a fault has been detected and the system has therefore been switched off • there is a fault in the ABS system • the system has been switched off manually. How the system works The Traction Control System (TCS) is designed to prevent wheelspin. This enables the car to achieve the best possible grip and, hence, maximum tractive effort, together with greater stability. The TCS uses information from the ABS wheel sensors to detect when the front (driving) wheels are rotating faster then the rear wheels. It then monitors whether one driving wheel is rotating faster than the other. If so, the faster wheel is retarded until both wheels are rotating at the same speed.