looking at your original part number i would have said you definately need to replace the IFZ as it would be the original module and is surprising it hasn't been replaced sooner, since you have replaced the IFZ and keys i'm starting to think you have a problem elsewere, either in the transponder coil (surrounds the ignition/starter switch) but i doubt, as this would cause fault code IFZ locked out?? or maybe the problem is with the CAN data wires, if you pull the CAN wires from IFZ and try to start the car and then check for fault codes this is what you get: CAN: no reception from IFZ. when you take your car back to the MB dealer ask the tech to check the CAN wires (Controller Area Network) and if it still has connectors on that CAN line get them cut out and have them soldered directly (a lot of CAN faults are caused by faulty connectors) as for the first fault CAN: TRANSM; from HFM n3/4 faulty. i can't really say, it could also be a CAN problem, this needs to be rechecked by your benz tech, if it has reoccured since you last had your car in (they should have cleared all fault codes and retested) then you need to start looking at CAN wires and their connectors. good luck