Turn the key and a small electric motor spins the engine fast enough to start combustion. That is the starter motor. It draws a huge current from the battery, often several hundred amps, for just a few seconds.

Before electric starters, drivers cranked engines by hand. It was tiring, dangerous, and sometimes broke wrists when the engine kicked back. Charles Kettering's self-starter on the 1912 Cadillac changed everything. The basic design, a series-wound DC motor with a drive pinion, has barely changed since.

How a starter works

• Ignition switch sends current to the starter solenoid.
• Solenoid engages a pinion gear with the engine flywheel.
• Motor spins the pinion, cranking the engine.
• Once the engine fires, the pinion retracts.
• A one-way clutch prevents the engine from spinning the starter.

Starters fail in predictable ways. A clicking sound usually means the battery is weak or the solenoid contacts are burned. A grinding noise suggests a worn pinion or damaged flywheel teeth. A slow crank points to a failing motor or high resistance in the cables. Replacement is straightforward on most cars, though some engines hide the starter under the intake manifold.