Ignition Coil Triggering
Control of the ignition coils is an output function of the MS S52 control module. The system is 100% solid state with no moving parts. The control module triggers each coil individually based on the parameters of engine speed and crankshaft position.
The ignition timing can be modified between each individual coil firing and can also be adjusted on a cylinder selective basis for knock control.
The power supply for the ignition coils is provided by a relay. This relay is identified as an "unloader relay" in the ETM and component listing displays.
The unloader relay was integrated into all vehicles starting with the 1997 model year. The purpose of this relay is to isolate the voltage supply as well as to relieve the ignition switch of the additional current draw needed by the ignition coils.
When KL 15 is switched on, the relay control circuit is provided power to close the relay providing operating voltage to ignition coils.