The O/D light is flashingin my 91 LS400. The tranny seems to be working fine, with no mishaps. The O/D switch works, and when it is switched on, the light starts to flash, but the car DOES go into overdrive. I have not noticed any problems thus far, but according to the manual, it is saying there is a major transmission failure. Anyone got any ideas, or know if there is a sensor out? Could it be the beginning of a transmission failure? Any help would be appreciated.