During the ETS practical exam, the candidate may be asked to diagnose a pre-configured installation set up by the trainer (fault finding), not only to program a new installation from scratch.

True. The KNX Basic practical exam syllabus lists error finding as an explicit competence, alongside topology, group address design, parameterisation and download. Examiners commonly seed the board with a typical defect — wrong physical address, missing group association, parameter mismatch on a flag, or a broken line coupler filter table — and ask the candidate to locate it within a time budget. Mastering the ETS diagnostic tools (Group Monitor, Bus Monitor, Device Info, Line Coupler filter table read-back) is therefore as important as building a fresh project.

Practise on a board that someone else has deliberately broken — self-built faults are too easy to spot because you remember where you cheated.