Heated Oxygen Sensor
WARNING: This page is about a different car, the 2002 Mazda Tribute, 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
Faults in Heated Oxygen Sensor (HO2S) or circuit should set a Diagnostic Trouble Code (DTC). See QUICK TEST in appropriate SELF-DIAGNOSTICS article.