Start-Stop System

Topics:

Introduction
Operation

Introduction:
The start-stop system shuts off the engine while standing still and restarts it the moment the driver wants to move again. This can occur while waiting at a traffic light or waiting for a bridge to open. A vehicle with a start-stop system falls under the category of “micro-hybrid.”

Legislation mandates that new passenger cars should not emit more than 130 grams of CO2 per kilometer on average during the legally established driving cycle. This driving cycle involves driving under various conditions and standing still. During idling, fuel is consumed, and CO2 is emitted, which is disadvantageous for the test. Passenger cars introduced to the market from 2012 onwards are therefore equipped with the start-stop system.

Vehicles equipped with a start-stop system often have a button on the dashboard to temporarily disable the system. In that case, the engine will not be shut off. On the next trip, the system is automatically reactivated. Permanently disabling the start-stop system is sometimes possible but not allowed, as the vehicle would then not comply with type approval.

Operation:
The start-stop system activates when the vehicle is stationary. This is detected by the wheel speed sensors (ABS sensors). In vehicles with an automatic transmission, the engine can stall when the brake pedal is continuously pressed. When the brake pedal is released, the engine starts, and the vehicle can drive away. In vehicles with a manual transmission, the gearbox often has to be in neutral, and the clutch must remain disengaged. As soon as the clutch pedal is pressed, the engine starts.

The start-stop system only activates if the following conditions are met:

Outside air temperature is above 3 degrees Celsius (may differ per brand).
Engine is at operating temperature.
Battery is sufficiently charged and at temperature. This is monitored using the intelligent battery sensor signal.
Driver’s seat belt is fastened.
Driver’s door is closed.
Hood is closed.
Vehicle is not on a slope.
Windshield defrost is not active.
Diesel particulate filter is not regenerating.
Front wheels should not be turned too far.
Trailer hitch is not connected to a trailer.

If these conditions are not met, a message often appears on the dashboard stating: “Start-stop system disabled,” or a symbol similar to the one in the image. When manually disabling the system using a button on the dashboard, this message also appears.