Trailer stabilisation helps to reduce the risk of the Audi A4 skidding when towing a trailer.
When is the trailer stabilisation system1) activated?
Trailer stabilisation is active when the following requirements are met:
- The ESC must be switched on Link and fully functional (no ESC malfunction).
- The trailer connector must be properly secured in the Audi A4 socket.
- The Audi A4 speed must be higher than approx. 65 km/h.
How trailer stabilisation works
In many cases, the driver can stabilise a swaying trailer by manually braking the Audi A4.
However, if the ESC detects that the trailer is swaying and this is affecting the towing Audi A4, it will automatically brake the Audi A4 in order to stabilise the trailer. The indicator lamp 
will flash in the instrument cluster. If possible, do not turn the steering wheel at this stage.
will flash in the instrument cluster. If possible, do not turn the steering wheel at this stage.In order to warn traffic behind you, the brake lights will come on during this automatic braking operation.
A trailer with a light load may sway quite considerably without the trailer stabilisation system intervening.
If the system for activating the trailer brake lights is defective, this will be indicated in the instrument cluster display Link.
Requirements for correct functioning of the trailer stabilisation system
If these conditions are not met in full, the trailer stabilisation system will only intervene to a limited extent or not at all WARNING!.
- The electrical connection between the towing Audi A4 and the trailer must be functioning correctly.
- The load on the trailer must be properly secured.
- The tyre pressures on both the Audi A4 and the trailer must be adapted to the load that is being carried.
- Where possible, operate the trailer with the maximum permitted draw bar weight.
- The trailer overrun brake must be set correctly. This is important to ensure that the trailer can be braked correctly, to avoid the Audi A4 and trailer "jack-knifing" and to prevent excess braking of the trailer.
- At low outside temperatures, both the towing Audi A4 and the trailer should be fitted with winter tyres.
It is essential that you adjust your speed to suit the weather, road and traffic conditions. Do not let the trailer stabilisation system tempt you into taking any risks when driving – this can cause accidents.
- The ESC and trailer stabilisation system cannot defy the laws of physics. This should be kept in mind, particularly on slippery and wet roads and when towing a trailer with a light load.
- The trailer stabilisation system is functional, regardless of whether the trailer has a mechanical overrun brake or not.
- The trailer stabilisation system is not always able to detect swaying of trailers with a light load.
- A trailer can still "jack-knife" on slippery roads with little grip, even if the towing Audi A4 is equipped with the trailer stabilisation system.
- Trailers with a high centre of gravity may even tip over before they start to sway sideways.
- If you are not towing a trailer, but the trailer socket is being used (e.g. for an illuminated bicycle rack), the trailer stabilisation system may be activated in extreme driving conditions.
- Please note the additional information and warnings Link.
1) Not available on Audi A4s for some markets.