Start and stop system


  • General
  • Health Benefits
  • Battery current sensor

With the start-stop system, the engine is switched off while stationary and restarted the moment the driver wants to start driving again. This can be while waiting for a traffic light, or waiting for an open bridge. A vehicle with a start and stop system falls under the category of “micro-hybrid”.

The legislation prescribes that new passenger cars may not emit more than 130 grams of CO2 per kilometer on average during the legally established driving cycle. This driving cycle consists of driving in different conditions and standing still. While standing still, fuel is consumed and CO2 is emitted, which is disadvantageous for the test. Passenger cars that came on the market from 2012 are therefore equipped with the start-stop system.

Vehicles equipped with a start-stop system often have a button on the dashboard with which the system can be temporarily switched off. In that case, the engine will no longer be switched off. The system is automatically reactivated on the next ride. Permanently switching off the start-stop system is sometimes possible, but not permitted: the vehicle then no longer complies with the type approval.

The start-stop system operates when the vehicle is stationary. This is registered by the wheel speed sensors (ABS sensors). Vehicles with an automatic gearbox may cause the engine to stall if the brake pedal is left depressed. When the brake pedal is released, the engine starts and you can drive off immediately. Vehicles with a manual transmission often require the transmission to be in neutral and the clutch disengaged. As soon as the clutch pedal is depressed, the engine starts.

The start and stop system will only operate if the following conditions are met:

  • Outside air temperature above 3 degrees Celsius (may vary by brand).
  • Engine is at operating temperature.
  • Battery sufficiently charged and at temperature
  • The driver's seat belt is in the belt buckle.
  • Driver's door closed.
  • Hood closed.
  • Vehicle is not on a slope.
  • Windshield defroster is not active.
  • Diesel particulate filter is not regenerated.
  • Front wheels should not be turned too far.
  • Tow bar is not connected to a trailer.

If these conditions are not met, a message will often appear in the dashboard with the message: “Start-stop system deactivated”, or a symbol like the one in the picture.

This message also appears when switching off manually with a button on the dashboard.

Battery current sensor:
The battery is loaded a lot more with a start-stop system. Not once, but several times per ride, the starter motor is actuated to start the engine. Because an AGM battery is more resistant to frequent discharging and recharging, it is often used in a car with a start-stop system. The state of charge is monitored by a sensor. This sensor is often referred to as an IBS (Intelligent Battery Sensor) or Battery Monitor System (BMS). This sensor is often mounted in the ground cable or on the negative pole. If the battery is too empty, there is a risk that the engine cannot be started, so the start-stop system will not operate. The start-stop system is disabled at a charge level that is less than 68%.

Inside the battery current sensor housing is a microchip with a controller that measures voltage, current, temperature and time. This data is often passed on to the comfort control unit (BCM) via the LIN bus. The BCM calculates the state of charge (State Of Charge, SOC) and the condition (State Of Health, SOH). An advanced battery current sensor also measures quiescent current. The state of charge of the battery is maintained at approximately 80%. After a certain time (eg 30 days) a regeneration process is started. The state of charge then goes to 100% by increasing the charge voltage to 15,2 volts. This prevents sulphation of the battery.

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