Signal Waveform
The HO2S requires a minimum temperature to provide a closed loop fuel control system. So HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions. The HO2S heater should be always ON after engine start. The ECM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the ECM provides a ground circuit for activating the heater. The left illustration is the signal waveform of HO2S Heater and the right is the one of HO2 sensor.