What is leaking in automatic cars

Automatic start-stop: This is how fuel-saving technology works

The automatic start-stop system in the car saves up to 15 percent fuel in city traffic. We explain how the fuel-saving technology works and give practical tips.

How does the automatic start-stop function?

A vehicle with an automatic start-stop has an automatic system to reduce fuel consumption. As soon as the vehicle is stationary, the engine is switched off. To do this, the gearshift lever must be in neutral and the brake pedal must be depressed. Modern vehicles sometimes switch off the engine while it is coasting.

Depending on the vehicle manufacturer, the engine will start again if eitherBrake pedallet go or partly additionally thatClutch pedal is kicked.

For vehicles with automatic transmissionthe engine switches off as soon as the vehicle is stationary or the speed falls below a certain minimum. It starts as soon as the brake pedal is released, the brake pressure falls below a defined level or the accelerator pedal is pressed - depending on the manufacturer.

Theelectrical systems work even with the engine stopped - unlike when the ignition key is switched off. If you do not want the engine to be switched off when the vehicle is stationary (e.g. when traffic is in line), this can be done by pressing a button"Auto off") can be prevented.

TheEnergy management of vehicles with automatic start-stop consists of various components. The main ones are the engine control unit including the start-stop coordinator, the battery sensor and a deep cycle battery with EFB or AGM technology.

When does the fuel-saving technology not work?

Depending onCar model and vehicle manufacturer there are various factors that prevent the automatic start-stop from working. Usually these are the following:

  • Battery voltage too weak

  • Outside temperature too low or too high

  • Engine not yet at operating temperature

Other causescan be:

  • Vehicle is on a slope

  • Indications that a driver does not want to wait, but wants to park: driver's seat belt buckle released, doors or bonnet opened, steering wheel turned strongly

  • Parking assistant activated

  • Trailer coupled

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What else influences the functioning of the system?

Frosty temperatures stress them out in winterbatterywhich is why the automatic start-stop system stops working in extreme cold. The lower temperature limit varies from manufacturer to manufacturer; it is usually in the range of plus three to minus five degrees.

Because of the high demand for electricity, for example in winterWindow and seat heating, in midsummer theair conditioning prevent the electronics from switching off the motor.

Some vehicles (e.g. Mercedes A-Class) only stop the engine automatically when thatVentilation fanis turned off. As soon as the engine has stopped, however, the fan can be switched on again without the engine starting (provided that the foot remains on the brake and is not engaged).

Is theStarter battery defective, it may only be exchanged for one approved by the manufacturer. The reason: The battery sensor must know the data of the starter battery used in order to be able to correctly determine its state of charge even with increasing age.

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