Very Quick Guide to Lambda Sensors

A lambda sensor is an electronic sensor that fits into the exhaust system. It is sometimes called an Oxygen sensor, O2 sensor, or AFR. Its purpose is to send a signal to the ECU to indicate how much oxygen is in the exhaust gases. This in turn indicates how efficiently the engine is running. The ECU uses this information to adjust the engine's fuelling as you drive.

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 (2005->) with a close-coupled catalyst have the sensor inside the engine compartment.

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.

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 if buying one.