Help EPC and motor A-class

Hi all, I need an advice about what could be happened to my car. I have an A-Class bought three years ago. Few days ago it stopped without a reason during the march, then the EPC led is turned on.
At Mercedes garage (of the city where I was) says me that the motor is broken and needs 6.000 euros to fix it (my car has 45.000 km!!!!!!!!!!!!!). O_O So I called my Mercedes garage and he says me that is not very probable, because EPC led concerns injector and not motor (on the other hand I have had service 5.000 km ago and I have no listen rumors when car has stopped to let me think that can be broken the chain of distribution)...
I'm so confuse! Please someone can explain me what is EPC? Yesterday I took car from that garage to take it here.... If really motor is broken is there something that can I do to evitate to pay 6.000 euros (car is out of warranty)?
Thanks Giulia
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