2 Lambda sensors... To be sure, to be sure

[pipnjones]

My new car has two lambda sensors. One is between the engine and the cat, and the other is after the cat. I don't quite see how the two bits of information could be effectively used together, unless it is a clue about carbon monoxide and NOx reduction...

The engine is a 1.6L Sigma for the European market.

Any ideas?

[CSR7]

Hope this helps http://www.lambdapower.co.uk/TechNotes/Tech-3.asp

[pipnjones]

Many thanks for the link. V interesting.

[Steve H]

Lots of very good info there but on a quick read-through I didn't see the answer to the OPs question amongst it!

Short answer is that the pre-cat sensor is the one used to adjust fueling and post-cat is there to monitor the efficiency of the cat.

[pipnjones]

You need to use the web link as a spring board to the other tech notes. The pic shows the sensor on this page, but is missing the relevant text. I cheated and went to the main page and into the Tech notes (Tech Note 1). Amongst other things, the newest EU rules mean that the engine has to be able to detect a failure of the Cat and it does this with the second probe. I think the two probes also mean the car can detect a failure of he Lambda sensor, and there will be other trickery, methinks.

The really interesting bits are how the ECU ignores the Lambda sensor at times, depending on what the motor needs to be doing, etc. They are cunning things... It beats repeated viewings of the News and Sport on the BBC website hands down.

[Steve H]

It becomes less involving when you do it for a job

TBH I did only skip-read the pages on the link but there was a lot of unusually accurate info on there