This mechanic that have been only guessing to what's wrong with my car and only have been hell, said i needed a new Abs module and he took one off his A4 idk what year and put it on my a6. Now the break light is flashing and ABS light is on. Does a module fron a A4 even fit on a A6?

 

It's probably the same unit, however the error codes probably need to be cleared. BUT.. if the ABS or any other error light is lit up, ALWAYS pull the OBD codes first before throwing parts at it. You'll need to find a shop that knows German cars and has a scanner that can connect to the other systems in the car besides the Engine Control Unit. An ABS light can come on for many reasons. Wheel sensor, loose wheel bearing.... Pulling the codes will tell you exactly where the issue lies instead of guessing which one of the many parts/sensors that make up the ABS system is at fault.