The primary current level method measures the current level in the primary circuit. The minimum and maximum current levels are used to turn the IGF signal on and off. The levels will vary with different ignition systems. Regardless of method, the Repair Manual shows the scope pattern or provides you with the necessary voltage reading to confirm that the igniter is producing the IGF signal.
Lack of an IGF on many ignition systems will produce a DTC. On some ignition systems, the ECM is able to identify which coil did not produce an IGF signal and this can be accomplished by two methods.
With the second method, the IGF signal is carried back to the ECM on a common line with the other coil(s). The ECM is able to distinguish which coil is not operating based on when the IGF signal is received. Since the ECM knows when each cylinder needs to be ignited, it knows from which coil to expect the IGF signal.
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