Ignition Control Module: Description and Operation

Ignition Coil And Power Transistor Circuit:

PURPOSE
The power transistor controls ignition current by interrupting the ignition coil primary ground causing secondary circuit discharge.

OPERATION
The engine control module (ECM) controls ignition timing through the power transistor. The power transistor is a switch that allows a very low voltage (from the ECM) to control a larger amount of voltage (negative side of coil). During engine cranking the ignition timing is fixed at 5°BTDC