Car Won't Start

What's happening

Most likely causes

1. 1

   Dead or weak battery

   The most common reason. Batteries last 3-5 years; a weak one may click or crank very slowly.

2. 2

   Corroded or loose battery terminals

   White or green crust on terminals blocks current even if the battery itself is fine.

3. 3

   Failed starter motor

   A single loud click with no crank, or grinding, often points at the starter.

4. 4

   Bad alternator (killed the battery)

   If the car died while driving or the new battery dies again quickly, the alternator is not charging.

5. 5

   Blown fuse or bad relay

   Starter and fuel-pump relays fail silently; a blown main fuse kills everything.

6. 6

   No fuel delivery

   Empty tank, failed fuel pump, or clogged fuel filter. Listen for the pump hum when you turn the key to ON.

How to diagnose it — in order

1. 1

   Turn the key and listen: rapid clicking usually means weak battery, one solid click points at the starter, silence points at fuses or the ignition switch.

2. 2

   Check battery terminals for corrosion and tightness. Clean with a wire brush.

3. 3

   Test battery voltage: 12.4V or higher is healthy, under 12.0V is discharged.

4. 4

   Try a jump start. If it starts and stays running, the battery was the issue; if it dies again, suspect the alternator.

5. 5

   Check the fuel gauge and listen for the fuel pump priming hum with the key in ON position.

Trouble codes tied to this symptom

If your scanner shows one of these, read its dedicated trouble-code page for the full diagnosis.