The ignition system is responsible for igniting the fuel/air mixture in the combustion chamber. This process needs to be carefully timed. The crankshaft position sensor senses the position of the crankshaft and sends a signal to the ECU of the vehicle. The ECU interprets this signal and sends a signal to the ignition coil to fire at certain times. The ignition coil sends high voltage through the spark plug wires to the spark plug, which ignites the fuel/air mixture.