Fuel pumps, diesel additive systems, injectors,absolutely anything to do with the Body control systems, electronic handbrakes,keys & transponders some mileage & service indicators,etc etc.
Certain german manufacturers are now using "pass-thru" technology where to unlock these codes you HAVE TO return your car to the main dealer , where they plug your car in & the ecu "talks" to Munich to get a diagnosis!
30 years selling parts in the motor trade Bud , seven of them selling Diagnostic products, its a minefield now & its only going to get worse !!