Denso Lambda sensors – reducing emissions

With demand for replacement Lambda Sensors increasing thanks to their growing role in emissions management, it has never been more essential to understand how vital a role they have to play. Here, Alan Povey of DENSO – part of the world’s largest OEM DENSO Corporation, shares some top technical tips on the role of Lambda Sensors.

What role do Lambda Sensors play?

A: In order to reduce emissions, modern cars have been designed to carefully control the amount of fuel they burn. The Lambda (or Oxygen) Sensor is a critical component in this process, Its goal is to work together with the car’s fuel injection system, catalytic convertor and electronic control unit (ECU) to achieve the lowest possible output of environmentally harmful engine emissions. The Lambda Sensor does this by monitoring the percentage of unburned oxygen present in the car’s exhaust gases. This data is fed to the car’s ECU, which adjusts the A/F (air/fuel) mixture. The correct air/fuel mixture enables the Catalytic Converter to run efficiently. This ‘exhaust gas cleaning system’ removes as many of the harmful emissions as possible from the exhaust before it leaves the car.

How exactly do Lambda Sensors work?

A: Lambda Sensors work together with the vehicle’s fuel injection system, Catalytic Converter and engine management system or electronic control unit (ECU) (Fig 1) to help achieve the lowest possible output of environmentally harmful engine emissions:

  • The Lambda Sensor monitors the percentage of unburned oxygen present in the car’s exhaust gases
  • According to whether the oxygen content in the exhaust gas is too high (a lean mixture) or too low (a rich mixture) the Lambda Sensor transmits a fast-changing, fluctuating voltage signal to the ECU
  • The ECU responds to this information by adjusting the air/fuel mixture entering the Catalytic Converter. The goal is to keep the air/fuel ratio very close to the ‘stoichiometric’ point, which is the calculated ideal ratio of air to fuel entering the Catalytic Converter. Theoretically, at this ratio, all of the fuel will be burned using almost all of the oxygen in the air. The remaining oxygen must be exactly the right quantity for the Catalytic Converter to function efficiently.
  • The Catalytic Converter then treats the exhaust emissions before they leave the car. Most modern cars are equipped with a three-way Catalytic Converter. ‘Three-way’ refers to the three regulated (harmful) emissions it helps to reduce – Carbon Monoxide (CO), unburnt Hydrocarbons (HC), and Nitrogen Oxide (Nox) molecules. The exact amount of oxygen in the exhaust gasses is important to the Catalytic Converter because it affects how well it is able to remove these harmful emissions from the exhaust gases. The right amount of oxygen enables a chemical reaction to take place between the harmful gases and the oxygen, resulting in harmless gases leaving the Catalytic Converter. If the converter is working correctly, all the oxygen in the exhaust gases will be consumed by this chemical reaction.

How often should Lambda Sensors be replaced?

A: DENSO recommends changing them as often as specified by the vehicle manufacturer. But Lambda Sensors should also be checked for functioning and efficiency at every vehicle check-up – an engine that’s old or showing signs of excessive oil consumption will need the Sensors changed at shorter intervals than specified.

To find out more about DENSO’s Lambda Sensors please call the DENSO Aftermarket Sales UK team on 02476 843416 or email

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