Did you auto identify the car from the Benz software; auto selection, READ under in screen and then should auto decode correct car.

After that did a full scan or went into control unit directly? You can do autoscan and after finishing the scan you enter the module (click on module and choose OK), then choose 'read codes'. And you should really have the codes in front of you, with (most of the time) good descriptions.

If you did a full autoscan and you go back to the main menu and you choose HISTORY, the last car will be on top of the list and if you select it (not the diagnostic button part, or you will go to car diagnostics, click above the blue car logo) you will have the car details together with all the codes from the autoscan.

Not all codes can be erased by the way, that is not due to MaxiSys issues but because Benz is just made that way, also if a code is wiring and immidiately checked by ECU it will be erased but set again before you can see it being gone.

-!- in red most of the time means MaxiSys could not identify the correct ECU and if you go into that selection/module/control unit itself you can still scan after selecting correct module/ecu yourself.

If all above was already known, my apologies.

 Matronix right. And ! doesn't mean that have error. In the OEM tool sometimes it show !, to. That means that the tool was not able to do a scan in that ECU.

  The system have to be check individually after clearing fault codes,

 The -!- means the MaxiSys could not identify the module (nr. or brand of it). It knows it is there but cannot read it by it self. Most of the time this is because there are several possible ECU's or other modules available on that carline and in that case, if the Sys cannot read it for itself, you have to go into the control unit itself and choose the right one. For instance, if you have Peugeot, you can have 3-4 different ABS systems for a certain car model; which you have to identify your self or just pick one after another and try to get into the module and read the codes (frustrating and this should be done better, but I'm sure Autel is working on that... ?).

If, like you experienced, you go into the module and you cannot read the codes, the MaxiSys recognises that there is a module, but cannot correctly communicate. This is something to mention to Autel, since they need VIN number etc. to identify the problem so they can improve on it.

It is an inconvenience that I understand may trouble you but gladly this is not happening too often and mostly on specific cars. I would love to help you more, but have no such car available to me right now to test this myself (not now at least).

 Can you identify the modules it tells -!-

I do have 2 cars - C320 CDI here right now. Although these propably are not 4-matic. You might want to choose manually a version that is closely related. I did scan these 2 C320 CDI mercs several times, since one needed general check up and reset after filter and oil change and the other is going into limp mode so extensive diagnostics used. These both are diesels however.