When do I have to change the sonda lambda?

Answer 1

When it becomes broken, of course. Sometimes they become badly worn, so it would be a good idea to replace it then.
Cmon now, you gotta be kidding, i never heard of such a part! But if it aint broken then you dont fix it!

Answer 2

I believe that is an oxygen sensor.
The oxygen sensor reads the fuel mixture in the exhaust.
rich ( fuel rich) or lean ( air or lean).
It should not have to be changed unless your indicator light
on the instrument panel is on and indicates a code in the
computer for the sensor. Periodically they do get contaminated
and need to be changed.