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What Is A Lambda Sensor

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A reply from Gjnorthall in one of the threads regarding Fuel consumption mentioned a duff Lambda Sensor.

What the heck is a Lambda Sensor,and more to the point what does it do, and if it needs replacing, because the fuel consumption on my 1998 RAV4 is blooming awful, how do I change it?


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It's a thingy located in the exhaust system that monitors the exhaust fumes/gases, looks a bit like a spark plug, i think i have successfully attached a link of one. They do get a bit sooty and they are not particularly cheap so it may be worth taking it out and cleaning it up first. Because they are in the exhaust and usually accessible from under the bonnet they tend to be a bit tight at times so you might need your WD40 to start with.

Regards Mike169


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The Lambda only gives benefits under steady state conditions such as cruising at a steady throttle opening. It does nothing when you accelerate so for short journeys / stop start town driving, it will do little in terms of fuel economy. If the Lambda fails - the engine warning light will illuminate. The Lambda and ECU work together in order to cycle the fuel mixture from rich to weak - it should do this about 8 times every 10 seconds. With age, sensors get sluggish, the ECU cannot cycle the mixture at the required frequency so control and therefore fuel efficiency is lost. Some things will kill as Lambda - in particular silicon (lubricating sprays and Oil additives) and antifreeze (failed head gasket).

There has been debate over the last couple of days about poor fuel consumption of petrol models - the effect of a duff Lambda if fairly marginal but condition of plugs, air and fuel filters is important.

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