Did your vehicle's check-engine light just pop on? An OBD-II scanner can provide some direction. We tested a handful to find ...

How to Use a Scan Tool There are countless scan tools on the market today. Some are available from major retailers for less than $30, while other, professional-grade offerings can cost thousands ...

OBD I engine management, dating back to 1980, used just one upstream O2 sensor, mounted in the exhaust manifold, as close as possible to the cylinder head's heat.