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Removing and installing switch for Audi hold assist (AHA) > < ABS/ESP Bosch 8.1 - overview

A4 Mk3

Audi hold assist (AHA)
Audi hold assist (AHA)
Some models are equipped with the Audi hold assist feature (AHA).
Function
This function assists the driver when the vehicle has to be held stationary, either frequently or for long periods, with the engine running.
When the Audi hold assist is activated after the vehicle comes to a standstill, it will hold the vehicle in a stationary position.
The driver can then release the brake pedal.
Initially the vehicle is held at a standstill by maintaining the brake pressure at all four wheels in the ESP system.
To prevent the ESP solenoid valves from overheating if the vehicle has to be held for long periods, the braking function is taken over automatically by the rear electromechanical parking brake if the temperature at the solenoid valves exceeds 200 °C.
The brakes are released automatically at a point determined according to the following factors:
t  Engine torque
t  Angle of gradient
t  Gear engaged
t  Manual gearbox: travel at clutch pedal detected by clutch sensor
t  Automatic gearbox: torque converter slip
To prevent the vehicle from rolling back, the brakes are only released when sufficient engine torque is available.
Activation
The following requirements must be met in order to switch on the „stand-by“ mode:
t  Driver's seat belt fastened
t  Engine running
t  Driver's door closed
t  No faults in ESP or electronic parking brake.
   
The function can then be activated by pressing the switch -2- in the centre console.
The switch indicates the status of the system:
t  Deactivated: LED in switch remains off.
t  Stand-by: LED in switch lights up
t  System active: LED in switch lights up and a green „P“ appears in the instrument cluster display
The electronic parking brake only takes over the braking function from the ESP when the green „P“ appears in the instrument cluster display and when:
t  The ESP solenoid valves reach a temperature of 200 °C,
t  The driver's door is opened,
t  The driver's seat belt is unfastened,
t  The engine is switched off,
t  The ignition is switched off,
t  The switch is operated,
t  The brake pedal or accelerator pedal is pressed,
t  The switch for the Audi hold assist function is operated without pressing the footbrake.
  Note
The green „P“ in the instrument cluster display changes to a red „P“ when the electronic parking brake takes over the braking function from the ESP.
  A46-10107

Removing and installing switch for Audi hold assist (AHA) > < ABS/ESP Bosch 8.1 - overview