Ignition System: Operation

Turn ignition switch to "ON" position, and battery positive voltage will be applied to primary winding of ignition coil.
When crankshaft position sensor signal is input to engine control module, ON-OFF control of ignition power transistor is performed by engine control module.
When ignition power transistor is turned on, current flows from ignition coil (primary winding) to ground through ignition power transistor.
When ignition power transistor is turned off, high voltage is generated in primary winding of ignition coil which induces even higher voltage in the secondary winding, causing a spark at the spark plug(s).