The linear O2 sensor is mounted on the front side of the Catalytic Converter (warm-up catalytic converter) or in the front exhaust pipe. It detects a wide range of air/fuel ratios in the exhaust gas from the rich to lean regions. This linear O2 sensor produces a current that corresponds to a specific air/fuel ratio. The PCM monitors this signal and determines whether the air/fuel mixture is rich or lean. The PCM constantly monitors the linear O2 sensor and increases or decreases the fuel injection duration using this signal. This is called closed-loop fuel control operation.

The PCM monitors front HO2S signal level during fuel cut-off to check plausability. The PCM sets DTC P2297 if front HO2S signal is out of the predetermined threshold. If the same error code is set in the next driving cycle, the PCM illuminates the MIL.