Stop & Start

Stop & Start: The technology that cuts the engine to save fuel

The Stop & Start system is nowadays a virtually ubiquitous technology on new vehicles. Designed to combat fuel waste and reduce the carbon footprint of automobiles, this device automatically shuts off the engine during stationary phases and restarts it almost instantaneously. Once reserved for high-end models, it has become widely democratized and constitutes an essential building block of modern eco-driving strategies.

How does the Stop & Start system work?

The operation of Stop & Start is managed by the vehicle's engine control unit (ECU), which continuously analyzes a multitude of parameters to decide whether or not to safely shut off the engine. The conditions for engine shutdown activation are generally:

• The vehicle must be at a complete standstill (zero speed).
• On a manual transmission: the gear shifter is in neutral and the clutch pedal is released.
• On an automatic transmission: the brake pedal is held depressed.
• The battery must have a sufficient charge level.
• The engine must have reached its optimal operating temperature.
• The outside temperature is neither too low nor too high so as not to compromise thermal comfort in the cabin (air conditioning/heating).

As soon as the driver signals the intention to move off again (pressing the clutch or releasing the brake), the system commands a reinforced starter motor to restart the engine in a fraction of a second, without the driver having to turn the key or press a button. To withstand these repeated cycles, equipped vehicles feature specific components, notably an AGM (Absorbent Glass Mat) or EFB (Enhanced Flooded Battery) technology battery and a more durable starter motor.

What are the concrete benefits of Stop & Start?

The main advantage of this technology is both economic and ecological. By eliminating unnecessary idling phases, Stop & Start achieves fuel savings of up to 5 to 10% in dense urban cycles, where stops are most frequent. This reduction in consumption directly translates into lower carbon dioxide (CO2) emissions, thereby helping to meet increasingly stringent environmental standards. Beyond these aspects, passenger comfort is also improved. The absence of engine noise and vibration when stationary creates a more serene cabin atmosphere, which is particularly appreciable in traffic jams.

Constraints and specific maintenance

Although very efficient, the Stop & Start system has a few constraints. It will not activate if conditions are not deemed optimal by the ECU in order to preserve mechanics and battery life. Most vehicles offer a deactivation button (often marked with an 'A' surrounded by an arrow) allowing the driver to switch it off manually if desired, for example in very choppy stop-and-go traffic. Regarding maintenance, it is crucial to replace the battery with an equivalent technology model (AGM or EFB). Installing a standard battery on a vehicle equipped with Stop & Start would lead to its very premature wear and system malfunctions. Although more expensive to purchase, these specific batteries are designed to last and withstand the demands of the technology.