The checks need to be mechanical. Code readers read codes. But (generally) codes only appear when there’s a fault

A big slippery field would be useful. But, to be honest, it’s so good at ‘just working’ it’ll be fine.
Just remember- never (ever) select off-road mode on tarmac as that
will break something. ‘On road’ mode actually means ‘choose 4x4 entirely automatically’. Off road mode forces 4 wheel drive but does not engage the (virtual) diff lock. That too only happens when the system feels it needs to. But it can only do that when off road mode is chosen. ELD only cuts in if one wheel is off the road and up in the air and spinning freely.
Better to read it this way:
Dial position 1 = auto 4x4 but no ELD available
Dial position 2 = permanent 4x4 and auto ELD if it’s needed (never select this on tarmac)
Dial position 3 = same as position 2,
plus hill descent control on a hill so steep you wouldn’t dare driving down it. For ‘normal’ hills (less than 1in 2), simply use 4x4 and engine braking. Never use on tarmac.
Note: Hill descent control only works if at least one wheel is turning. It is not likely to work on ice or very slippery mud as, with all four wheels sliding, the wheel sensors say ‘oh, none of the four wheels are turning… I must be parked’