Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
The Ignition Control (IC) module sends signals that PCM requires for fuel control and spark advance calculations. At start of engine crank, IC module controls spark advance (by-pass mode). When the second 3X reference pulse is recognized by PCM, PCM applies 5 volts to by-pass circuit, commanding IC module to switch spark advance to PCM control (IC mode). If PCM detects an open in the IC circuit, DTC will set. Engine will start and may run in by-pass mode timing. DTC will set when engine is running and PCM detects an open in by-pass circuit.