Very Quick Guide to Lambda Sensors

A lambda sensor is an electrical device that fits into an exhaust system where we want to measure the Oxygen content of the gas. This could be in a road vehicle or industrial machine, for example a boiler or furnace. It is sometimes called an Oxygen sensor, O2 sensor, or AFR sensor. Its purpose is to send a signal to the ECU (engine control unit) to indicate how much oxygen is in the exhaust gases. This indicates how efficiently the engine is running. The ECU uses this information to adjust the engine's fuelling as you drive.

Lambda sensors can also be used for industrial applications, such as electricity generating stations and biomass boilers, and for general O2 measurement for industrial processes, eg. welding, steel rolling mills, drying ovens, furnaces. In industrial settings, a PLC (programmable logic controller) is used to control the sensor.

What happens if it fails?

MOT emissions failure, excessive fuel consumption, catalyst failure, poor performance, engine check warning light, fault codes are all symptoms that can be associated with Lambda sensor failure. The Lambda sensor's efficiency deteriorates over a period of time.

Maintenance

No maintenance of the Lambda sensor is required and there are no serviceable parts. Similar to a spark plug, when it's worn out it should be replaced.

Where is it?

Mounted on the engine exhaust manifold or exhaust pipe, or under the vehicle for the rear sensor. Modern engines with a close-coupled catalyst have the sensor inside the engine compartment. A close coupled catalyst places the catalyser very close to the engine to shorten warm-up time and reduce emissions.

Cars made after year 2000 have at least two sensors, front and rear, and are termed OBDII compliant. Multiple sensors enable the ECU to better judge the efficiency of individual cylinders. Some cars have up to four sensors.

How can I replace it?

Firstly consult our fitting guide - it's roughly the same as fitting spark plugs. Or get your garage to do it. Some garages will not fit 'universal' type sensors, please check with them first before buying one. Direct fit sensors are more expensive, but are preferable to the universal types. This is because the sensor is tailored to each application, and the ECU may perform a check to ensure the correct part is fitted.