Sondas Lambda

Lambda probes



LThe 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 indicate 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 sensor element. When heated, it develops an electrical potential difference between its surfaces depending on the amount of oxygen.
  • Platinum electrodes cover the internal and external surfaces of the ceramic, allowing the generated voltage to be measured.
  • Protective layer and metal mesh Filter particles and protect the ceramic from dirt and excessive heat.
  • Heating element Rapidly raises the sensor temperature to approximately 300–600 °C, the range required to obtain accurate readings from start-up.
  • Connector and wiring. It usually includes two wires for the output signal and two for powering the heater. In some designs, the vehicle chassis acts as ground.

Types of lambda probe

  • Narrowband (binary) Only indicates whether the mixture is rich or lean, with a signal oscillating between low and high values.
  • Broadband (Linear) Provides a continuous and more accurate reading of the air-fuel ratio, useful in advanced control systems.

Location and duty cycle

  1. The first sensor is located before the catalyst to measure the initial mixture.
  2. A second sensor, in modern engines, is placed behind the catalytic converter to verify its effectiveness.
  3. During closed-loop operation, the ECU maintains the probe voltage at a stable midpoint, indicating a perfect mixture.

The lambda sensor is essential for electronic engine management and emissions control. A functioning sensor ensures fuel economy, optimal power, and compliance with environmental regulations.