The CMP sensor tells the Engine Control Unit (ECU) where the camshaft is in its rotation. The ECU uses this information, along with information from the crankshaft position sensor (CKP sensor), to precisely time fuel injection and ignition. Without this crucial timing information, the engine won't know when to fire the spark plugs or inject fuel, resulting in a misfire or complete engine failure to start.
While you might be able to crank the engine, it won't run consistently, or at all, without a functioning camshaft position sensor.
