Why won't my car start?

If the engine cranks but doesn't fire: usually fuel, spark, or a failed crankshaft/camshaft sensor. If it doesn't crank at all (just clicks or silence): almost always the battery, starter, or a bad connection. A dead 12V battery is by far the most common cause across both scenarios.

Cost range: $0–$800. Severity: high. Safe to drive? N/A — car isn't moving. Get a free battery test at any auto parts store before spending money on parts.

Most likely causes

1. 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. ($120–$300 (battery), common)
2. 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. ($300–$700, common)
3. Bad battery terminals / corroded connections — White/green crust on the terminals. Clean with baking soda + water and re-tighten — often a free fix. ($0–$30, common)
4. 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. ($150–$500, less common)
5. 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. ($400–$1,200 (pump), less common)
6. 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. ($50–$300, rare)