Ignition Control Module: Description and Operation

Ignition System Component Layout:

PURPOSE AND LOCATION
The ignition power stage unit (# 5 in image) functions as an electronic switch that opens and closes the coil primary ground connection. This function is comparable to the operation of the points in a mechanical ignition system. The power stage unit is located on the ignition coil on the firewall.


OPERATION AND SIGNAL
The ignition power stage unit consists of a power transistor and integrated circuit. It is used to make and break the primary circuit, and to regulate the current through the ignition coil. It receives a triggering signal from the ECU. The ECU applies power to the output stage, which turns it ON. In this ON state, current flows through the primary circuit of the ignition coil. When the ECU determines it's time for a spark, the power to the output stage is momentarily interrupted. The transistor turns OFF, breaking the primary circuit, and inducing a high voltage spark in the secondary circuit. The ECU regulates the duration of the interruption in the trigger signal, and thus regulates the dwell angle, and charging time. The longer the interruption, the smaller the dwell angle and the shorter the charge time.