Reasons for the Failure of the Start-Stop System

Driving is more economical and environmentally friendly with start-stop technology. As a result, by 2020, one in every three vehicles on our roads will be equipped with this technology. For example, if a car comes to a complete stop at a traffic light, the start-stop system turns off the engine. The engine restarts as soon as the clutch pedal is pressed again, or the brake is released in the case of an automatic transmission.

In addition to the frequent engine starts required for this process, the battery also powers all electronic consumers even when the engine is turned off. For modern vehicles, the car battery could be considered the system's heart. It is frequently aided by an intelligent Battery Management System (BMS), which serves as the car's electronic brain. The failure of the start-stop system could be attributed to the interaction of these two vital systems.

The start-stop function is disabled by the battery management:

The most important function of any battery is to start the engine. If the battery only has a low charge, the Battery Management System (BMS) disables the start-stop function, allowing the engine to start. A similar protective mechanism is at work in the following situations:

The incorrect battery technology was used, which can only provide a limited number of charging cycles.

The temperature outside is either too high or too low. If the battery requires too much power to power the fan, the start-stop function is disabled. When and whether this occurs is determined by the comfort settings of the specific car manufacturer. It is also possible that the start-stop function is still supported, but the air conditioning system is reduced automatically.

The engine temperature is either too hot or too cold. If the engine is not heated by consumers or the battery, it must generate its own heat through combustion, necessitating a higher starting current. As a result, the start-stop function is disabled. If the engine overheats, it must be cooled by the radiator fan because the airstream is insufficient or does not exist when stopped at traffic lights. Because the fan requires a large current, the start-stop function is disabled.

The use of the incorrect battery technology causes issues:

Another possibility is that the battery was not properly registered by the vehicle when it was replaced. For example, if the technology or battery capacity is incorrectly entered, the BMS will not be able to use the correct algorithm. If the battery is not even registered as new by the vehicle, it is possible that it is not detected as new and thus its full potential is not utilized.

More information on this topic can be found in our article on the dangers of replacing a Start-Stop Battery with a conventional battery.

Factors that is unrelated to the battery

There are also non-battery-related factors that disrupt the start-stop function:

  • The seat belts are not being used.
  • The vehicle's doors or hood are not properly closed.
  • The parking attendant is working.
  • The car is climbing a steep hill (gradient too large)

If the start-stop function frequently fails or does not function at all, it is best to visit a workshop as soon as possible. In this case, the experts can determine whether the battery needs to be replaced using a free battery test.