This gets repeated on every thread on this topic but from what I've read is not true and heavily favors VW. VW was caught actively faking the test results by having the ECU detect it's being tested and change its settings. What every manufacturer has been caught doing is optimzing for the test and not getting the same results in real world conditions. That's a fault of the test and is perfectly legal. The only guilt of the manufacturers is lobbying to not upgrade the test.

IIRC Mercedes wasn't caught cheating they just got in trouble because they use the same engine control units which contain the routines that make cheating possible.

Mercedes was entering an allowable disclosed higher emission mode with an unallowable, undisclosed, entry condition.

In EPA terminology, a defeat device.

Mercedes was already ordered to recall affected models.