Car Won't Start: Causes & Fixes
Reviewed by the Wrenchit.ai editorial team · Last reviewed · Editorial standards
Causes ranked by likelihood
| Cause | Likelihood |
|---|---|
| Dead or weak 12V battery — Lights dim, dashboard flickers, or you hear a rapid clicking when turning the key. Most batteries last 4–6 years. Jump-start to confirm. | Most likely |
| Failed starter motor — Single loud click and nothing happens, even with a known-good battery. Tap the starter with a wrench while someone turns the key — if it starts, the starter is dying. | Possible |
| Bad battery terminals / corroded connections — White/green crust on the terminals. Clean with baking soda + water and re-tighten — often a free fix. | Possible |
| Failed crankshaft or camshaft position sensor — Engine cranks but won't fire. Often P0335, P0340, P0016, or P0017 stored. No spark + no fuel injector pulse = sensor. | Less likely |
| Empty fuel tank or failed fuel pump — Cranks but won't start. Listen for the 2-second fuel pump prime when you turn the key to ON. Silence = pump. | Less likely |
| Anti-theft / immobilizer fault — Security light flashes and engine cranks but won't fire. Try the spare key. Reprogramming is dealer-only on many cars. | Less likely |
How to narrow it down
- Note when it happens. Record speed, temperature, and whether braking, turning or accelerating triggers it.
- Scan for codes. Plug in an OBD-II scanner — a stored code narrows the cause quickly.
- Check: Bad battery terminals / corroded connections. White/green crust on the terminals. Clean with baking soda + water and re-tighten — often a free fix.
- Check: Anti-theft / immobilizer fault. Security light flashes and engine cranks but won't fire. Try the spare key. Reprogramming is dealer-only on many cars.
- Check: Dead or weak 12V battery. Lights dim, dashboard flickers, or you hear a rapid clicking when turning the key. Most batteries last 4–6 years. Jump-start to confirm.
- Check: Failed crankshaft or camshaft position sensor. Engine cranks but won't fire. Often P0335, P0340, P0016, or P0017 stored. No spark + no fuel injector pulse = sensor.
- Check: Failed starter motor. Single loud click and nothing happens, even with a known-good battery. Tap the starter with a wrench while someone turns the key — if it starts, the starter is dying.
- Check: Empty fuel tank or failed fuel pump. Cranks but won't start. Listen for the 2-second fuel pump prime when you turn the key to ON. Silence = pump.