Exhaust Gas Control (Peugeot 405)

In order to minimize the amount of pollution that enters the atmosphere, some models are equipped with a catalyst in the exhaust system. On all models with a catalytic converter, the system is closed-loop, where a lambda sensor in the exhaust system feeds back data to the ignition and fuel injection system of the ECU, allowing the ECU to adjust the mixture to provide the best conditions possible for the catalyst to operate.

The lambda sensor has a built-in heating element, controlled by the ECU via a relay, in order 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 with the amount of oxygen in the exhaust. If the air-fuel mixture is too rich, the exhaust gases have a low oxygen content and the sensor sends out a low voltage signal. The increase in voltage occurs when the mixture is lean, when the amount of oxygen in the exhaust gases increases. The maximum efficiency of complete and correct combustion of fuel occurs if the mixture "air-fuel", supplied to the engine, is maintained in the chemically correct ratio for the complete combustion of gasoline - 14.7 parts by weight of air to 1 part of fuel ("stoichiometric" attitude). The sensor output voltage changes over a wide range at this point, the ECU uses the signal changes and corrects the mixture "air-fuel", supplied to the engine by changing the pulse width of the fuel injector (length of time when the injector is open).