Ignition Relay: Description and Operation

Component Overview:

Ignition Coil Power Transistor:

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

Location
The power transistor is located on the intake manifold under the ignition coils.

Operation
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. During engine cranking, the ignition timing is fixed at 5°BTDC.