Exhaust gas monitoring (Peugeot 405)

In order to minimize the amount of pollutants released into the atmosphere, some models are equipped with a catalytic converter in the exhaust system. On all models with a catalytic converter, the system is of a closed type, where the lambda sensor in the exhaust system reports data to the ignition and fuel injection system ECU with constant feedback, allowing the ECU to adjust the mixture to provide the best possible conditions for the catalyst to operate.

The lambda sensor has a built-in heating element, controlled by the ECU via a relay, to quickly warm the tip of the sensor to operating temperature. The tip of the sensor is sensitive to oxygen and sends a voltage to the ECU that varies depending on the amount of oxygen in the exhaust gas. If the air/fuel mixture is too rich, the exhaust gas has a low oxygen content and the sensor sends a low voltage signal. The voltage increases as the mixture becomes leaner, increasing the amount of oxygen in the exhaust gas. Maximum efficiency for complete and proper combustion of fuel occurs if the air/fuel mixture supplied to the engine is maintained in the chemically correct ratio for complete combustion of gasoline - 14.7 parts by weight of air to 1 part of fuel (the "stoichiometric" ratio). The sensor's output voltage varies over a wide range at this point, the ECU uses the signal changes and corrects the air/fuel mixture supplied to the engine by changing the pulse width of the fuel injector (the period of time when the injector is open).