Lambda Sensors

Lambda sensors detect oxygen concentration levels in the combustion mixture, helping burn fuel more efficiently and control emissions.

Lambda Sensors

How lambda sensors work

The air-fuel mixture in an engine’s combustion chamber can affect how hot, how quickly and how cleanly the fuel burns. For optimum combustion, the air-to-fuel ratio needs to be within a certain window. For specific driving conditions, the engine may run in sub-optimal conditions. For example, to be more fuel efficient, the engine may run on a ‘lean’ mixture. In contrast, to deliver high power performance, the A/F mixture needs to be ‘rich’. Such specific mixtures cannot be maintained for a long period of time without risking excessive emissions or even causing damage to the engine or the catalytic converter.

Lambda sensors work constantly to keep the air-fuel ratio correct by monitoring the quantity of unburned oxygen in the exhaust gases and feeding this information back to the electronic control unit (ECU), which can then dynamically adjust the air-fuel mixture to keep it close to the ‘stoichiometric point’ – the ideal ratio at which the catalytic converter will function optimally and keep emissions to a minimum.

Lambda sensors can in fact fulfil two roles: regulating sensors, placed before the catalytic converter, and diagnostic sensors, fitted after the catalyst as an extra layer of security to ensure the converter is doing its job.

DENSO’s range of proven OE-quality lambda sensors is optimised for the widest possible car parc coverage with fewer part numbers, making part sourcing easy for distributors and workshops.

DENSO lambda sensors overview image

Features and benefits

  • Plays a central role in reducing fuel consumption and improving engine efficiency.
  • OE standard of quality and reliability.
  • Multiple housing and fitting types available.
  • Improving technology helps lower emissions and meet regulations.
Proprietary technology
DENSO has been developing lambda sensors since the 1970s and has been responsible for several leaps forward in sensor technology. Some technologies, such as the A/F Sensor type that meets EURO 3 and tighter regulations, are exclusive to DENSO.
High build quality
Premium materials and construction methods, along with unique protective features such as the ‘double trap’ layer surrounding the sensing element, keep DENSO Lambda Sensors free of issues for longer.
Optimised range
Thimble and planar types, linear and switched sensors, and different housings and fittings are all available as part of a ‘smart consolidated’ range with minimal risk of installation errors.

Types and characteristics

The DENSO Lambda Sensor range is designed to maximise aftermarket coverage without requiring workshops to carry prohibitive amounts of stock. Many types of sensor are available.

Lambda Sensors types

O2 sensors

A conventionally functioning sensor, which uses oxygen ions passing through the sensing element to generate a high-low switching voltage. Available in thimble type (offering precision measurements) and planar type (with the heater integrated into the sensor, offering faster start-up time).

DENSO O2 sensor product number DOX1598
A/F sensors

Pioneering sensor technology with a linear current output, giving oxygen quantity readings and not just a binary ‘high’ or ‘low’. This allows the ECU to make far more precise adjustments. Both thimble and planar types are available to the aftermarket.

DENSO AF type sensor product number DOX 0590

To ensure a reliable connection, we offer two lambda sensor fitting types: direct fit sensor, with OEM connector fitted for easy installation, and universal fit sensor without a connector so you can reuse the old one.


DENSO Lambda Sensors are available in two choices of OE quality housing: screw-type and flange-type. Whatever you choose, the housing is ready to fit as the original, right out of the box – there is no need for adaptors.


DENSO lambda sensors are of a consistently high quality, with protective components such as corrosion-resistant stainless housing, 100% gas-tight seal, self-cleaning properties and porous PTFE membranes.

Catalogues and leaflets

To find out more about Lambda Sensors browse the Downloads Area section. Click here.

Installation and fault finding

Correct installation and regular checks and replacements are recommended to keep lambda sensors functioning as intended. Follow our guides for best practice. Check the Download section for more information.


To install a lambda sensor safely and correctly, always follow the part instructions and manufacturer guidelines. We have compiled some general advice to help you succeed:
  • Disconnect the sensor and free the wiring from any fixings before turning the sensor.

  • Use a flare spanner with six contact points to create more grip than a conventional open-ended spanner.

  • Apply short strokes to break the seized connection.

  • Use penetrating fluid and give it time to enter properly.

  • If you are sure the sensor will be replaced, cut off the wire and use a long 22mm socket.

  • Apply heat locally (preferably by induction, not open flame).

  • If needed, clean the thread in the exhaust pipe with a cleaning tap.

  • When the thread of the sensor does not have anti-seize lubricant pre-applied, DENSO supplies a small bag of anti-seize compound. Apply this moderately to the thread. Make sure to keep the nose clean. Tighten the sensor to the prescribed torque, using a wrench with a suitable lambda sensor socket. Take care not to damage the wires.

  • Cut the new sensor wires to length. The new sensor with the old connector must be the same length as the old sensor and connector originally.

  • Strip the wire ends to a length of 7mm.

  • Crimp the butt-splices with a ratchet crimping tool with a red die (size 22-16).

  • Shrink the insulation of the butt-splices with the hot air until they are sealed.

  • Follow the same steps as a direct fit sensor above

Fault finding

As a result of sensor contamination or damage lambda sensors can start operating out of specifications. When this happens, the ECU can recognize inconsistent signals, and ignore the its feedback completely. The engine will start running in an “open loop” mode and the check engine light will come on. Other symptoms that can be related to malfunctioning oxygen sensors are an increased fuel consumption (up to 30%) and uneven running engine. Also, the problems can be discovered during a emission test, indicating excessive levels of HC and CO, for example. For more detailed diagnostic tips, please sign up for our webinars or e-learning courses.