Fault code 0219, GLXI 1.6 -00

Just bought fault code reader "Memo scanner"

It gives me fault code

0219 "Lambda control"

Any basic advise for this fault code ?

Can I measure on front and back lambda sensor to determine which one that is faulty ?

Or can it be ECU ?

Any advise will make me happy.

Basically the car is fine. Just slightly uneven on idle. Like 10 sec fine and the 3-5 sec mildly uneven.

PS As newbie in forum, I hope this is the proper section for my car DS