The Lambda sensor,installed at the exhaust manifold, is planar ZrO2 dual cell type 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 the engine maximum loading condition. The ECM/PCM 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) : The ECM/PCM supplies pumping current to Lambda sensor (+pumping current) and activates it for Lambda sensor to have the characteristic at λ=1.0 (0.0 pumping current). With the value of pumping current supplied to Lambda sensor, the ECM/PCM detects O2 density of exhaust gas.Rich air-fuel mixture(0.9<λ<1.0) : The ECM/PCM takes away pumping current from O2 sensor (-pumping current) and deactivates it for Lambda sensor to have the characteristic at λ=1.0 (0.0 pumping current). With the value of pumping current taken away from Lambda sensor, the ECM/PCM detects O2 density of exhaust gas.This performance is the most active and fast at normal operating temp(450°C~600°C). Thus, in order to reach normal operating temp, and last at that temp, the heater(heating coil) is integrated with the Lambda sensor.

The heater coil is controlled by the ECM/PCM as PWM. The resistance of the 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, Lambda sensor temp is measured and the Lambda sensor heater operation varies based on the data.

The HO2S(Heated Oxygen Sensor) is used to supply the ECM/PCM with information regarding the composition of the air/fuel mixture. The HO2S is positioned in the exhaust pipe ahead of the TWC. To measure the oxygen content, the HO2S requires a supply of ambient air as a reference. Since this is supplied through the wiring, the lead must not be clamped or damaged in any other way. The HO2S produces a voltage that varies between 0.1V and 0.9V under normal operating conditions. The Engine Control Module (ECM/PCM) monitors this voltage and determines if the exhaust gas is lean or rich. If the voltage input at the ECM/PCM is under approx. 0.45V the exhaust is lean, and if the voltage input is over approx. 0.45V the exhaust is rich. The ECM/PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary.