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.

As your car ages and accumulates mileage, its O2 sensor readings can drift too far from the ECU’s expected values. When this occurs, it triggers the check engine light and stores an OBD-II code.