Lambda probes for cars
Emission control and fuel economy
The lambda probe is an oxygen sensor installed in the exhaust system of gasoline and diesel engines. Its purpose is to continuously measure the oxygen concentration in the combustion gases. Based on this information, the engine control unit (ECU) adjusts the air-fuel mixture to maintain the ideal (stoichiometric) ratio, optimizing efficiency and reducing polluting emissions. When the engine burns fuel, the exhaust gases contain a variable amount of oxygen. The lambda probe generates a voltage proportional to this concentration. Values close to 0.2 V indicate a lean mixture (excess air), while around 0.8 V indicates a rich mixture (excess fuel). The ECU interprets this signal and corrects the injection timing and duration. Main components: Zirconium or titanium ceramic: Acts as a sensing element. When heated, it develops an electrical potential difference between its faces depending on the amount of oxygen. Platinum electrodes: Coat the inner and outer faces of the ceramic, allowing the generated voltage to be measured. Protective layer and metal mesh: Filter out particles and protect the ceramic from dirt and excessive heat. Heater resistor: Quickly raises the sensor temperature to around 300–600°C, the range required for accurate readings from start-up. Connector and wiring: Typically includes two wires for the output signal and two to power the heater. In some designs, the vehicle chassis acts as a ground. Lambda sensor types Narrow-band: Indicates only whether the mixture is rich or lean, with an oscillating signal between low and high values. Wideband (linear): Provides a continuous and more accurate reading of the air-fuel ratio, useful in advanced control systems. Location and duty cycle The first sensor is located before the catalytic converter to measure the initial mixture. A second sensor, in modern engines, is located after the catalytic converter to verify its effectiveness. During closed-loop operation, the ECU maintains the sensor voltage at a stable midpoint, indicating a perfect mixture. The lambda sensor is essential for electronic engine management and emission control. A sensor in good condition ensures fuel economy, optimal power, and compliance with environmental regulations.
