O2 sensor installed at exhaust manifold is linear O2 sensor and it senses O2 density of exhaust gas for accurate EGR control through fuel correction. It also limits smoke which is generated by reach air-fuel mixture at engine maximum loading condition. ECM controls pumping current in order to fit λ-value from linear O2 sensor to 1.0.

Lean air-fuel mixture(1.0＜λ＜1.1) : ECM supplies pumping current to O2 sensor (+pumping current) and activates it for O2 sensor to have the characteristic at λ=1.0 (0.0 pumping current). With the value of pumping current supplied to O2 sensor, ECM detects O2 density of exhaust gas.

Rich air-fuel mixture(0.9＜λ＜1.0) : ECM takes away pumping current from O2 sensor (-pumping current) and deactivates it for O2 sensor to have the characteristic at λ=1.0 (0.0 pumping current). With the value of pumping current taken away from O2 sensor, ECM detects O2 density of exhaust gas.

This performance is the most active and fast at normal operating temp.(450℃~600℃) thus, in order to reach normal operating temp. and last at that temp., heater(heating coil) is integrated with O2 sensor.Heater coil is controlled by ECM as PWM. The resistance of heater coil is low when coil is cold thus, current through it increases while resistance is high when coil is hot thus, current decreases. With this principle, O2 sensor temp. is measured and O2 sensor heater operation varies based on the data.