I tried to understand how it works with relays as y columbo25 explained, start and stop cars have two relays in serial, and both should be on to activate the starter solenoid that run the starter motor.
The body computer do some advanced diagnostic to avoid stuck relays by the way.
But even dealing with activating the start motor did not solved the problem : turning the ignition key on, activating the starter motor playing with relays and no start. It's like no spark or no fuel injection, engine did not start at all.
So deactivating start and stop looks not activating ECU any more.
Looks really complicated, if someone has more information, schematics please help !
