The starter motor is a powerful electric motor attached to the transmission bell housing. When you turn the key or press the start button, a solenoid engages a pinion gear with the engine’s flywheel. It spins the engine physically to begin the internal combustion cycle. Because it requires a massive amount of amperage to turn a cold engine, it is directly connected to the battery. If the starter fails, the engine will not crank at all, often resulting in a single loud “click” noise.