Heated Oxygen Sensors (HO S)

WARNING: This page is about a different car, the 2007 Mazda B3000. However, it is still accessible from the selected car via links, so may be relevant.

The HO2S provide the powertrain control module (PCM) with voltage and frequency information related to the oxygen content of the exhaust gas. In addition to providing the PCM with indications of how rich/lean the engine is operating, the upstream HO2S signal serves as an input to the HO2S monitor. The downstream HO2S signal is an input to the Catalyst Efficiency monitor. The downstream HO2S may be located after the light off catalyst or underbody catalyst. The underbody catalyst may be in-line with the light off catalyst, or the underbody catalyst may be common to two light off catalysts, forming a "Y" pipe configuration.

Fig 1: Three-Way Catalytic Converter Nuts With Torque Specifications

Courtesy of MAZDA MOTORS CORP.