Diagnostics An oxygen sensor that’s going bad or has failed altogether won’t always throw a check engine light or trip a diagnostic trouble code. Sometimes if there’s an internal problem ...

We drill holes in an exhaust header to demonstrate how even the tiniest exhaust leak can affect O2 sensor accuracy and yield unreliable tuning data.

The oxygen sensor was replaced but the 'check engine' light won't go out. Now what? Which octane fuel is best? AAA's Car Doctor has answers.