The traction control system prevents the driven wheels from spinning when the car is accelerating.

General notes

The traction control system (ASR) is one of the functions incorporated in the electronic stabilisation program (ESP).

The traction control system (ASR) helps the car to start moving, accelerate and climb a gradient in slippery conditions where this may otherwise be difficult or even impossible.

How the system works

The ASR acts automatically i.e. without the driver's intervention.

With the aid of the ABS sensors, the ASR monitors the speed of the driven wheels. If the wheels start to spin, the engine power is reduced automatically to match the amount of grip available.

The system works at all speeds.

The ASR works in conjunction with the ABS. If a malfunction should occur in the ABS, the ASR will also be out of action.

Switching on

The ESP is switched on automatically when the engine is started and performs a self-test routine. As soon as this routine is complete, the system switches back to normal operating mode. If the traction control system (ASR) has been deactivated (for one of the reasons noted below) you can switch it back on manually by pressing the switch ⇒ fig. 192. The message ESP/ASR on will appear briefly in the display.

You can switch the traction control system (ASR) on again if necessary by pressing the switch ⇒ fig. 192.

Switching off

If required, the ASR can also be switched off manually by pressing the switch briefly ⇒ fig. 192 (for less than 3 seconds). The ESP warning lamp lights up when the traction control system (ASR) is switched off. The message ASR off will appear in the display. The ASR can be deactivated at any speed.

The traction control system should normally remain switched on at all times. It should only be switched off manually in particular circumstances where a certain amount of wheel slip may be desirable.

For example:
• when driving with snow chains
• when driving in deep snow or on loose surfaces
• when rocking the car backwards and forwards to free it.

The ASR should be switched on again afterwards as soon as possible.

Note
To ensure that the ASR works properly, all four wheels must be fitted with identical tyres. Any differences in the rolling radius of the tyres can cause the system to reduce engine power when this is not desired. Also refer to “Replacing wheels and tyres”.