Car Won't Start? A Click-by-Click Diagnostic
When a car won’t start, the sound it makes when you turn the key narrows the cause fast. A single click points to the starter or battery connection; rapid clicking points to a low battery; cranks but won’t fire points to fuel, spark, or a sensor; and dead silence points to the battery, ignition switch, or a safety interlock.
Start here: what happens when you turn the key?
| What you hear | Most likely cause |
|---|---|
| Rapid clicking | Weak or dead battery, or a bad connection |
| One loud click, no crank | Failed starter motor or starter solenoid |
| Engine cranks but won’t fire | No fuel, no spark, or a crank/cam sensor fault |
| Nothing at all (dead silent) | Dead battery, ignition switch, or safety interlock (clutch/brake/park) |
| Starts then immediately dies | Anti-theft, idle-control, or fuel-delivery issue |
Step 1 — Check the battery first
Most no-starts are battery-related. Turn on the headlights: if they’re dim or dead, charge or jump the battery. If they’re bright but the car still won’t crank, the battery probably isn’t the cause — move on.
Step 2 — Cranks but won’t fire
If the engine spins but won’t catch, it’s missing one of three things: fuel, spark, or correct timing. A failing crankshaft or camshaft position sensor is a common culprit — see P0335 (crankshaft sensor) and P0340 (camshaft sensor). Low fuel pressure (weak pump) is the other big one.
Step 3 — Dead silent
No click at all usually means no power to the starter: a fully dead battery, corroded terminals, a bad ignition switch, or a safety interlock. On a manual, press the clutch fully; on an automatic, make sure it’s in Park and try Neutral.
Want it narrowed down for your exact car? Ask the AI Mechanic free → — tell it the sound and symptoms and get the most likely cause ranked for your year, make, and model.
Related trouble codes
- P0335 — Crankshaft Position Sensor Circuit
- P0340 — Camshaft Position Sensor Circuit
- P0300 — Random/Multiple Cylinder Misfire
Browse the full OBD2 code library or the AI repair database.