4-in-1 Diagnostic Guide - includes OBDII Guide, Sensor Guide, Emissions Guide, Diagnostic Trouble Code Guide. Sensor Guide is a comprehensive learning tool that gives you the knowledge you need to understand what happens under the hood of today's cars. How sensors, work, what they do, how to tell when they're bad and common failure symptoms. Information you need to diagnose and repair your own vehicles. Don't replace parts until you know you've made the correct diagnosis!

[U.S. only]