This document summarizes the goals and key points of Module III which covers oxygen sensors, scopes, and oxygen sensor testing and analysis. The main topics are: 1) The different types of oxygen sensors including heated, unheated, titania, and zirconium sensors and how they react to exhaust oxygen levels. 2) How zirconium and titania sensors produce a voltage signal in response to exhaust oxygen levels. 3) How to set up an analog or digital scope to analyze oxygen sensor waveforms and the characteristics of different types of electrical signals. 4) The criteria for a good oxygen sensor including minimum and maximum voltage levels and switching frequency.