This module covers the theory, operation, and testing of the four main O2 sensor types encountered in the field: conventional zirconia, titanium, lean air/fuel (wideband tandem), and the Toyota-style air fuel ratio sensor. For each type, you'll learn how the sensor works, what a good waveform looks like, and how to approach testing it with a scope or scan tool.

Additional topics include:

• Zirconia sensor contamination sources and the "characteristic shift down" failure mode
• How wideband sensors extend feedback control beyond stoichiometry
• Why flatlined waveforms are normal on wideband sensors
• How EGR interacts with fuel control differently on speed density vs. MAF systems