For most modern cars even a basic scan tool is not enough. You need proper diagnostics specific to the car just to do routine maintenance. I've seen someone nearly scrap a car because it was not running properly after a cambelt change. The garage didn't know that you had to do a "phonic wheel" (Cam /crankshaft reluctance sensor) re-learn after changing the belt. They wanted £300 to take the head off and look at the valves. Literally 3 minutes with a laptop and CAN interface sorted it.
If the PC diagnostics are not enough Pico Technology's PC based 'scopes do CAN and other serial protocols, even ARINC 429) as standard and their "Automotive" range has comprehensive diagnostic software for anything from poor compression (using just a DC Clamp ammeter on the battery lead, think about it) to suspension and transmission faults by vibration analysis.
Was scammed by a car sales shithead in Emden. They sold a RR Discovery with a broken air suspension (which would not have been the problem). The real problem was that some italian hot shot managed to put in an ECU which was not programmed to the car, meaning that there was a VIN mismatch in 4 ECUs (the RR Discovery 3 has 23 ECUs in total) and RR does not provide reprogramming. If you try to program in a spare suspension compressor, the ECU will crosscheck the VINs and, if it finds a mismatch, will brick the car by activating the anti theft instant boat anchor program.
RR offered to swap out ALL ECUs (at up to 2500 quid a piece, that would have been a real bargain). To get access to some specific programming options, I would have had to drive the car (with the defunct air suspension) to London to some special RR shop to get some dudes to reflash those microcontrollers with an in system programmer.
Great.
This was a total write off. Either would have been a no go as the costs far exceeded the value of the car.
I am praying to Thor to smite that Emden guy with his hammer (or throw a meteor onto Emden, which ever is easier).
So now I have this specific car tester (Autel MD806)
https://www.ebay.de/itm/Autel-MD806-Pro-Profi-Diagnoseger%C3%A4t-f%C3%BCr-45-Fahrzeugmarken-ALLE-SYSTEM-OBD2-MD808/183843777999?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649which I am taking along to every used car I look at. Found a couple of used cars that would have been real bad deals, so this thing has already paid for itself.
It does to crosschecking of error codes in all ECUs and is vendor specific and multi protocol. It also allows to reset oil change intervals and initiate catalytic converter cleaning cycles.
All in all, highly recommended for quick inspection of used cars and all those things you need advanced diag for. It does not do programming though, the programmers are ten times as expensive.