Lambda reading

[jsoap]

On my DW10CD 2.0 Peugeot Expert diesel, the "Mixture calculated by the O2 sensor" default reading is 0.099 when the engine is off.
Since no units are specified I'd expect 1 to equal a ratio of 14.7, with a value below 1 indicating lean conditions
In practice this figure reads mainly between 0.25 and 0.65 (mostly at the higher end) - so that would indicate AF in the range 22 to 60
I've seen lambda readings being defined in other ways, and just wanted to know if my assumptions look right.
Thanks

[xantia_v6]

I think that it is more likely that lambda = 1 equates to a stoichiometric mixture with an air/fuel ration of 14.7:1

[RichardW]

It's a diesel, so 14.7 doesn't necessarily apply, and it's not trying to control an exact mixture. I think O2 sensors on later diesels are to ensure there's sufficient excess oxygen to burn the soot off. Have you actually got an issue, or just trying to understand the readings?

[xantia_v6]

It's a diesel, so 14.7 doesn't necessarily apply, and it's not trying to control an exact mixture. I think O2 sensors on later diesels are to ensure there's sufficient excess oxygen to burn the soot off. Have you actually got an issue, or just trying to understand the readings?

14.5:1 for diesel, see: https://x-engineer.org/automotive-engin ... rformance/

[jsoap]

It's a diesel, so 14.7 doesn't necessarily apply, and it's not trying to control an exact mixture. I think O2 sensors on later diesels are to ensure there's sufficient excess oxygen to burn the soot off. Have you actually got an issue, or just trying to understand the readings?

Thanks, that's my understanding also, but I just wanted to be sure that I was reading the right values - it just seemed a little counter intuitive higher reading = lower ratio.
I do have an issue with black smoke at idle and (lots) at acceleration, and a couple of garages have suggested that the ecu may have been remapped.
So I'm looking at the requested fuel & air ratios and what the O2 sensor measures. They seem to line up and don't indicate a rich mixture.