on new mercedes benz they have a gateway module unit which needs to communicate to germany but thats only used when you are writing something to the car like a replacement , ECU, EIS, TCU or SAM - some tool vendors support this too, Snap-on, Bosch etc.
for regular repair any decent scan tool and a decent oscilloscope is used without issue. You can pay to buy wiring diagrams and you are set!
Teshtlemp ustaad will screw up these cars if they probe 12V into a 5V circuit.
OR
start replacing control units because of "no communcation" errors without actually seeing if the bus network is down or garbled - usually its a pretty straightforward but slightly lengthy diagnosis if bus is down. - oscilloscope is required to test the bus.
Educated approach to them makes them very easy.
e.g. old BMW headlamp off issue - repair is as follows
1 test bulb
2 test supply
3 test wiring
4 test switch
(all above are plain basic)
new BMW with "active" headlights - bulb out - repair is as follows
1 test bulb and grounding etc.
2 connect scanner and probe front lighting module
3 send ping to headlights
4 see if command from switch is appearing at module - comes from switch and light sensor too with auto headlamps.
5 see if module is processing command and sending it out
etc etc.
the second steps 2 and down are all done while sitting inside car with laptop or scanner to finalize the repair if HID ballast and ignitor are bad.
imagine if "lektishann" told owner to buy "nawee toob/bulapp" for about Rs 20K and it still doesnt work. Thats why a thorough diag is done before some part is condemned.
