Oxygen sensors are a product that have been around for more than 20 years, yet most motorists don't even know they have one or more of these devices on their vehicle - let alone what it does.

The only time customers even become aware of oxygen sensor existence is if they get a Check Engine light and there's a code that indicates an O2 sensor problem or their vehicle fails an emissions test because of a sluggish or dead O2 sensor. If their engine isn't running well or is using too much fuel, somebody might tell them they might need a new O2 sensor. But in most cases, they won't have a clue as to how to diagnose or test this mysterious little device that is often blamed for all kinds of driveability and emissions ills. That puts the sales knowledge on the service technician.

You can explain to the fuel savvy customers the importance of replacing defective O2 sensors - and it need not be too complicated. Tell them an O2 sensor monitors the fuel mixture so the engine computer can adjust the air/fuel ratio to maintain the lowest possible emissions and best fuel economy. The O2 sensor does this by reacting to unburned oxygen in the exhaust. The sensor generates a small voltage signal (usually less than 1 volt) that increases when the air/fuel mixture goes rich, and drops when the air/fuel mixture goes lean. It acts like a rich/lean switch that signals the computer every time the fuel mixture changes, which is constantly....