Crankshaft Position Sensor

What it does

The crankshaft position sensor is like a hall monitor for the engine — it watches the crankshaft spinning and tells the ECU (the engine's brain computer) exactly where each piston is at every moment. The ECU uses this signal to fire the spark plugs and inject fuel at precisely the right time. When this sensor fails — especially when it gets hot — the ECU loses its position reference and either fires everything at the wrong time (engine misfires and runs rough) or stops firing altogether (engine stalls or won't start). It's a small sensor but it controls everything.