Why does Audi indicate that the auto start-stop is unavailable?

[StHarper]

Start-stop system failure is not necessarily a fault of the auto start-stop system itself; it could be due to issues with the braking system or air conditioning system, among others. A specific repair plan can only be provided after a comprehensive analysis using a diagnostic tool to read fault codes and data streams in conjunction with the fault symptoms. Generally, faults in the auto start-stop system do not affect the normal driving of the vehicle. Below is an introduction to relevant information: 1. The function of the auto start-stop device is typically controlled by the engine management system. This device can be installed in both manual and automatic transmissions. During the engine shutdown process, when the vehicle encounters congestion or a red light, the driver presses the brake until the vehicle stops and keeps the brake pressed without releasing it. 2. In addition to operating the clutch, shifting gears, and braking according to conditions, the driver must also meet several other requirements, such as the engine speed being below 1200r/min, coolant temperature between 25°C and 100°C, brake vacuum above 550mbar, battery temperature greater than or equal to -1°C but less than 55°C, and the difference between the set air conditioning temperature and the actual air outlet temperature being below 8°C.

[Hannah]

The Audi I drive has also been frequently showing this 'auto start-stop unavailable' prompt recently, probably you've encountered it too. This system is quite sensitive and often automatically shuts down due to minor issues. For example, when the battery charge drops below 70%, it disables the start-stop function to protect the electrical system. Last winter during a long drive, I got the prompt—turns out it gets disabled when temperatures are too low or too high, causing engine instability. Also, when the AC is cranked up too high, it shuts down to save power. If there's an issue with the braking system, like sensor faults or inaccurate wheel speed data, it can trigger this prompt too. I’ve taken it to the shop a few times, and they found blown fuses or the battery needed charging. Don’t delay fixing this to avoid nighttime driving risks. Regular maintenance like replacing the battery every two years and using a high-quality charger can reduce these faults.