How many lambda probes does the CUPA engine have? 

Does it have two or only one ? (before the cat).

I'm getting an error on B1 S1, so that should be the one upstream of the cat? (like the one here ? Replacing Lambda Sensor Skoda Octavia 2014 - YouTube )

Just one, judging from the wiring diagram.  Designated G39, which is normally pre-cat.

Yeah, that's right. You triggered some "hidden" memory I had apparently(by bringing the wiring diagram in discussion and G39 naming). I remember from the self study pdf on ea288 engines, that there's only one pre-cat.

 

When replacing the sensor, should I reset the learned values ?

Yes. If you do not do it it takes around 200km to work itself out.

On 13/07/2021 at 12:20, BogdanB said:

When replacing the sensor, should I reset the learned values ?

 

On 16/07/2021 at 13:55, alextz said:

Yes. If you do not do it it takes around 200km to work itself out.

And how pray tell does one do that?

Sensor can be reset via VCDS - module 01.

If it sorts itself out within 200km, is it worth bothering?