Symptoms of a malfunctioning NOx sensor include increased fuel consumption, as well as reduced power and acceleration. If a sensor fails, it will also trigger an on-board diagnostic (OBD) code, ...

These symbols, often called "idiot lights," are aimed at being easy to understand. But for many drivers, young and old alike, it's not that easy.

Mass air flow sensors fail most often in cars but a $20 air filter replacement every 12,000 miles prevents the $250-400 repair bills most drivers face.