Engine Cranks But Won’t Start

Why “cranks but won’t start” is really three questions

If the starter spins the engine but it won’t run, the engine is missing one of three things: spark (gas), fuel, or the timing signal the computer needs to fire either one. A diesel adds a fourth: enough compression/heat to light the fuel (glow plugs when cold). The questions above split those apart fast — a no-pump-hum points at fuel, a security light points at the immobilizer, and on a diesel the presence or absence of white smoke tells you whether fuel is even reaching the cylinders.