Heated Oxygen Sensors (HO2S)

WARNING: This page is about a different car, the 2005 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

The HO₂ S 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 HO₂ S signal serves as an input to the HO₂ S monitor. The downstream HO₂ S signal is an input to the Catalyst Efficiency monitor. The downstream HO₂ S 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: Removing Bolts - With Torque Specification
Courtesy of MAZDA MOTORS CORP.