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The latter of course.
Something may be broken with the fan, radiator itself or with the wiring.
For example, you see (via App) that the ECU has switched the fan to HI speed, and the radiator is still on low / first speed, or it is not spinning at all.

Are you Really asking? ;) For example, because diagnostics consists in checking (using the interface and software) whether the status of devices and parts behaves in accordance with a certain logic ;) An example of logic (chart; cooling fans speed depending on...) is attached (source: google). Kindl...

I know.

But why not LOW or HI? Sometimes during diagnostics (for example A/C) we want to know which specific speed has been activated and when

Micra K12, 2003, gasoline | NDSII Lite v1.53 (Android)

Parameter / Register: Radiator – Fan Speed / Mode: Why only OFF/ON not OFF/LOW/HI?
Because, from what I know (via “Facory Service Manual”) and I experienced, ECU is serving OFF, LOW and HI
?

Regards.