Will a faulty crank position sensor keep car from starting?

Yes, a faulty crank position sensor can absolutely prevent a car from starting. The crank position sensor tells the engine control module (ECM) where the crankshaft is in its rotation. The ECM needs this information to know when to fire the spark plugs (in gasoline engines) or inject fuel (in both gasoline and diesel engines). Without this crucial information, the engine won't know when to ignite the air/fuel mixture, resulting in a no-start condition.