The Audi start/stop system is designed to save energy and reduce CO2 emissions by automatically turning off the car's engine when the vehicle is stopped (at a traffic light or drive-thru, for example), and starting it back up before the car starts moving again. The system uses a heavy-duty starter and a deep-cycle battery designed for the repeated starting required when the system is in use.
When the car comes to a stop and the driver selects neutral and releases the clutch, the engine is automatically switched off. When the driver depresses the clutch again the engine automatically starts and the car can be driven away. The start/stop function only works when the hood and driver's door are closed, the driver is wearing their seat belt, the vehicle has been driven faster than 2.5 mph before stopping, and when the vehicle is not pulling a trailer. The engine may not automatically be switched off (or may be switched back on) if the engine temperature is too low, the outside temperature is very high or very low, the air conditioner is on, the windshield is being defrosted, power consumption is too high, or the battery is low. The system is automatically enabled when the car is started, but can be disabled by pressing a button.