How a Car Starter Works: The Starting System Explained

What happens when you turn the key

1. You turn the key, or press the start button with your foot on the brake.
2. The car checks that it's safe to start: an automatic has to be in Park or Neutral, and a stick shift needs the clutch pressed. On cars with an anti-theft system, the key or fob has to be recognized too.
3. A small signal goes to the starter relay and the starter solenoid, which act like a heavy-duty switch.
4. The solenoid does two things at once: it pushes a small gear on the starter out to mesh with the big toothed ring on the engine, and it sends full battery power to the starter motor.
5. The starter motor spins the engine. Once the engine fires and runs on its own, you let go of the key and the starter gear pulls back out.

Battery and cables: the starter uses more power than anything else on the car, so it needs a strong battery and clean, tight cables.
Ignition switch or start button: sends the "start" signal.
Neutral safety switch or clutch switch: keeps the car from starting in gear.
Starter relay and solenoid: switch the big current on to the starter.
Starter motor: a strong electric motor that turns the engine over.
Flywheel or flexplate: the big toothed ring on the back of the engine that the starter gear turns.

Rapid clicking: usually not enough power reaching the starter, like a weak battery or bad connections.
One click, then nothing: a dead battery or a failing starter. If a jump doesn't change it, suspect the starter.
No sound at all: a completely dead battery, a bad connection, or a problem in the start circuit, like the shifter not fully in Park.
Grinding: the starter gear isn't meshing right with the engine. Stop and get it checked, because it can chew up both.
Whirring, but the engine doesn't turn: the starter motor is spinning, but its gear isn't catching the engine.
Cranks fine but won't start: the starting system is doing its job. The problem is usually fuel, spark or the anti-theft system.

Make sure it's all the way in Park, or try starting in Neutral with your foot on the brake.
Check that the battery terminals are clean and tight.
Turn the headlights on and try to start. If they go very dim or out, it's the battery or a connection. If they stay bright and you hear one click, it points more toward the starter.
Don't keep cranking over and over. It drains the battery and can overheat the starter.

Won't start? We find the real cause and replace starters right where the car sits.