Ignition Control Module: Description and Operation

PURPOSE/OPERATION
The power transistor controls ignition current by interrupting the ignition coil primary ground causing secondary circuit discharge. The ECM controls ignition timing through the power transistor. The power transistor is a type of switch that allows a very low voltage (from the ECM) to control a larger amount of voltage (negative side of coil). It is actually three power transistors combined into one unit, controlling each circuit of the triple ignition coil.