Ignition Control Module: Description and Operation

Fig. 94 Power Transistor:

The power transistor unit, located at the back of the cylinder head, is a low current switch. It allows the signal sent from the ECU (very low current) to activate the primary circuit in the ignition coils (much higher current). This induces high voltage in the secondary windings of the coil, providing spark at the spark at the plugs. There are four power transistors in the unit.