Hi have the same issue

I have a 2007 renault megane automatic, at least twice a day, it makes a loud bang, the check gearbox message appears and the car goes into limp mode, once i turn the car off and on again the car runs fine?

Luis, August 2015

Yep check the computer it will you the two regulating valves need replacing , the banging sound is caused by to much pressure taking the spools valves in the valve body ,the older type valves have cream/white coloured plastic tops on them the newer types have black or blue tops , even if you replace them your self you still have to get the software up graded or its back to square one !

ferkemall, October 2015

These cars are problematical ,people seem to think that they can run on dex 2 or 3 they can't cope on this because they run hot ONLY USE FULLY SYNTHETIC FLUID ,look in the manual reno say to long in traffic,to long on the motorway or to much weight ,they go on to say you may have to replace the thermostat with on of a lower value,
All points to overheating the fluid .

Pressure regulating solinoids are a common problem £500 is not uncommon and the software has to be updated if they are replaced

The French idea of a sealed for life trans unit is its downfall they it lasts for life yet every other mfg says change the fluid at 30,000
Debris from the clutches and the steels cause wear on bearings,bushings,seals and valve body components like solinoids

Flush it out and put a couple of extra magnets on the metal pan !
I have a modus so I know
Goodluck with it .

peter hicks, August 2015

Your best bet is to get it onto the correct computer to see what faults are stored.

cdc, August 2015