i have a 525i 92 model that recently went for a gearbox overhaul after gears started slipping and eventually wouldnt drive forward .now after the overhaul the car takes uses 2nd gear for take off n dr

It sounds like your transmission is in limp home mode. This could two issues a bad rebuild and the internal issue could have occured. Or yes it is possible the module failed but I wouldn't try that yet. In the module there is a computer chip called a eprom (erasable programmable read only memory) BMW had a SIB (service information bulletin on replacing this eprom with an updated part. But this is only after checking some of the shift solenoids. The link Tom has given you is a good read and at the bottom has very good information about the resistances of the solenoids of the transmission. Your other option is to let the dealer scan the system for faults and then go from there for what it might be. Hope some of this helps.