Antilock Brakes / Traction Control Systems: Description and Operation

Audi Hold Assist

Depending on the model, the vehicle may be equipped with Audi Hold Assist (AHA).

Function

The function assists the driver if the vehicle must remain stopped frequently or for long periods of time when the engine is running.

When the vehicle is stopped and the function is activated, the vehicle is held in place by Audi Hold Assist (AHA).

The driver can release the brake pedal.

The vehicle is held in place by maintaining the brake pressure on all four wheels in ESP.

To prevent the ESP solenoid valves to overheat when stopped for long periods of time, the rear electro-mechanical parking brake automatically takes over braking when the solenoid valves reach a temperature of 200 °C.

The point when the brakes automatically release is based on the following information:

• Engine speed

• Angle

• Gear engaged

• Automatic transmissions, through converter release

To prevent the vehicle from rolling back, the brakes are only released when there is sufficient engine torque.

Activation

The following conditions must be fulfilled to switch the "stand by" function on:

• Driver wearing seat belt

• Engine running

• Driver door closed

• No ESP and electronic parking brake malfunctions.

The switch - 2 - in the center console activates the function.





The switch indicates the operating conditions.

• Deactivated - the LED in the switch is off.

• Stand by - the LED in the switch is on.

• Active - the LED in the switch is on and the instrument cluster display shows a green "P".

Braking function is only transferred from ESP to the electronic parking brake if the "green P" in the instrument cluster is visible and if:

• Solenoid valves in ESP have reached a temperature of 200 °C

• Driver door is opened

• Driver seat belt is unlatched

• Engine is stopped

• Ignition is switched off

• Switch is operated

• Brake pedal or gas pedal are pressed.

• Audi Hold Assist switch is operated without pressing the brake.

• When braking function is transferred from the ESP to the electronic parking brake, the instrument cluster display changes from a "green P" to a "red P".