The most critical sensor on the engine is the engine speed sensor, without this sensor the ECU would not know that the engine is moving and therefore it would never fire a spark nor inject any fuel. The ECU gets information from the crankshaft and camshaft position sensors in the form of electrical impulses over a period of time. When the ECU knows what pulses to expect it can compare this to what pulses it receives and determine the engine speed and position at any point in time. There are two main types of sensor used for this application;