Start & stop function: Why doesn’t the engine stop?

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The start & stop automatic can also be switched off in almost every vehicle.

More and more vehicles already have one as standard Start & stop function for the engine. The way it works is almost always the same: if you pull up to a traffic light, shift into neutral and take your foot off the clutch, the engine stops. As soon as you depress the clutch again, it automatically starts again. This function is also useful in traffic jams high savings potential. Roughly speaking, the start&stop function is worth it from about 10-15 seconds, during which the engine is off. There is usually complex technology behind a start & stop function, so there are several reasons why the Motor sometimes does not turn off:

Why the engine doesn’t always switch off

  • The engine has not yet its operating temperatur (about 50 degrees is sufficient) is reached. In winter, when temperatures are below zero, you often notice that the engine only switches off after about 20-30 minutes of driving time
  • the interior temperature is too high/too low: If it is too hot inside in the summer, the air conditioning has to work. This only works with the engine running
  • The vehicle is not completely in standstill
  • The driver is not belted
  • the battery level is OK
  • The driver’s door is not closed
  • Stop and go traffic: The vehicle has been driven at a speed below 5 km/h since the previous engine stop

Why the engine starts again automatically

  • The interior heats up when the air conditioning is switched on
  • Low brake vacuum due to repeated brake actuation
  • Vehicle rolled (speed > 5 km/h)
  • Battery charge too low due to long engine stop phase

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