This module continues the diagnostic case study approach using real-world ignition system failures on GM 2.5 and 2.0 four-cylinder engines. A key theme throughout is the importance of not assuming a repair is complete, and recognizing when a vehicle has multiple unrelated faults contributing to the same symptom.

Topics covered include:

• Interpreting ICM current waveforms when crank sensor access is unavailable
• Identifying failed coil drivers within the ICM using current probe analysis
• How a loose power connection can cause ICM malfunction during cranking
• Distinguishing between ICM and coil failures using primary current signatures
• Understanding EST (Electronic Spark Timing) failure, Code 42 diagnosis, and how the bypass circuit affects EST signal amplitude on the scope
• Using dynamic scope testing as an alternative to the static ohmmeter-based factory trouble chart procedure
• Practical recommendations on OEM vs. aftermarket ICM reliability