Ignore the hype: the C3 Stop & Start isn’t the first car to cut its engine in traffic for the sake of economy and emissions. The clever part is that it uses very few components that are different to a standard Sensodrive C3, which means the cost is kept low.
A 2KW reversible alternator performs the functions of both starter motor and alternator, which reduces the noise on start up and the time it takes the engine to fire.
Driving on open roads you’ll notice no difference, but with the brake pedal depressed below four mph the Sensodrive clutch opens, the engine cuts out and a green ‘eco’ indicator illuminates on the dash.
Lift your foot from the brake, the engine starts and the C3 scoots away. The air-con and all electrical accessories still function with the engine off, although the engine will run constantly if the cabin/exterior temperature difference becomes too great for the air-con to cope with, battery power begins to suffer or the engine gets too cool. There’s also a switch to override the system.
The only real drawback is the need to keep your foot on the middle pedal when stationary, even with the gear selector in neutral and the handbrake on, which can be a pain.