ECU and EGR problem

[telc1999]

I have a 2007 Megane CC 2L diesel (150hp) and last month the EGR valve failed (stuck open I believe). Got it replaced and within 5 miles the check engine light came on and check emissions on the dash. The garage pulled off an EGR sensor code from the system and eventually discovered that the ECU was only sending 1v to the EGR. The garage sent the ECU away to be told after 2 weeks that it wasn't faulty. This week (not having had the car for 2 weeks so far) an outside specialist has tried remapping the ECU which has failed and tomorrow he is coming back with a Renault specialist to spend what will be a 3rd day looking at it since the ECU was returned allegedly not the problem. Does anyone have any insight as to what is wrong with the car?? My garage are running out of ideas!