Heated Oxygen Sensor (HO2S)

All models are equipped with a primary heated oxygen (HO2S-1) and secondary heated oxygen (HO2S-2) sensors. They are located in exhaust before and after the catalytic converter. These sensors measure quantity of oxygen left in exhaust gas after combustion. ECM uses signal from HO2S-1 to adjust air/fuel mixture and HO2S-2 to monitor converter efficiency by comparing readings from both sensors. HO2S-2 is also used to correct for minor faults in HO2S-1. If voltage signals from both sensors are the same, ECM sets a DTC and turns on CHECK ENGINE light, indicating that catalytic converter is not affecting oxygen content of exhaust. The electric heating element built into each sensor provides improved cold engine driveability, and ensures that HO2S operating temperature is maintained all the time.