Look at the additional information to be gained from consideration of a third gas, oxygen (O2), the “lean indicator.”

To keep things interesting, perhaps we can look forward to hunting for oil leaks that refuse to drip on anything except a clean piece of paper on the owner’s garage floor.

Got one of those treadwear pattern charts on the wall of your shop? The ones with the different patches rubbed on the business edge of the tire, with corresponding diagnoses in the chart blocks? Guess what? Many of them are wrong.

This article goes a step further and discusses some basic points on reading electronic system diagrams.