Function Explanation (DTC Detection Outline)

WARNING: This page is about a different car, the 2017 Mazda 3. However, it is still accessible from the selected car via links, so may be relevant.

The PCM monitors the oxygen storage amount proportional to the catalytic converter purification characteristic.
The PCM starts to monitor after recovery (fuel injection starts) from fuel cut control.
The PCM temporarily changes the target air/fuel ratio to rich at fuel cut recovery, and detects the response time until the HO2S output signal outputs the voltage on the rich side.
If the catalytic converter purification characteristic deteriorates, the amount of the time until the HO2S detects the voltage on the rich side is shorter compared to the normal purification characteristic. (refer to the following figure) The PCM detects a catalytic converter malfunction using this characteristic.

Fig 1: HO2S Output Signal Timing Waveform

Courtesy of MAZDA MOTORS CORP.