This module introduces two ignition systems from different development backgrounds, using them as vehicles to develop diagnostic strategies and scope techniques that apply broadly — not just to these specific systems.

Tom covers the GM DIS (distributor-less) ignition system in detail, including how the ignition control module interacts with the crank sensor, reference signal, EST, and PCM. Key diagnostic concepts include:

• Non-floating vs. floating ground sensors and why test point selection matters
• Action/reaction testing and the importance of keeping channels as close together in the circuit as possible
• Using trigger strategy to capture intermittent failures without babysitting the scope
• Recognizing ICM failure types: reference failure, primary failure, and EST failure
• Reading secondary information embedded in a waveform, such as coil current ramps visible on the reference signal
• Understanding pull-up vs. pull-down circuits and how that affects diagnosis

The emphasis throughout is on building a repeatable diagnostic process rather than memorizing system-specific procedures.