Owners of 2011-2015 Audi A8 and 2012-2015 Audi A6 or A7 vehicles may note that the engine cannot be switched off, with warnings on in the instrument cluster (ABS/ESP, etc.).
In case of loss of speed signal due to control module failure, it may not be possible to switch off the ignition by only pressing the START ENGINE STOP switch when the vehicle is in Park and the brake pedal is applied. In this case, the ignition can only be switched off with the emergency-off function.
The emergency off function prevents the engine from being turned off if the START ENGINE STOP button is mistakenly pressed while the vehicle is being driven. The ABS control unit establishes a speed signal. The speed signal determines whether the vehicle is moving or standing still. If no speed signal is present and a standstill cannot be recognized, the ignition can only be switched off with the emergency-off function which is activated at speeds below 6 mph when the START ENGINE STOP button is held down and the brake pedal is pressed at the same time.
Another scenario involves winter driving. The drive wheels may operate with different revolutions for some time due to a constant slip. The ABS control unit can interpret this as implausible wheel speed and deactivate the ABS, even though there may be no system error.
After the ignition is switched off and the engine is restarted, the system is fully active again. Because of the temporary ABS deactivation and missing speed signal, the ignition can only be switched off with the emergency-off function. This is normal system function.