code 42 please help baffled

[cel]

hi i have a supra 1993 auto
i had a diagnostics done which came up code 42 on this as the od light blinks all the time when driven or stays lit if i press it.
my car was in a specialist tuning garage that deal with all jap cars
they tested all the sensors (all clear) tried a new ecu unit still code 42 done a few other tests and said i needed a new convertor new speedometer
had a new one fitted still the od light blinks
they have now done another diagnostics level 1 to 10 i think they said and they have come up with a voltage fluctuation on the overdrive and i need a new piece between the gear box and engine torque i think they said
if anyone else has had a similar problem or know anything about this subject then please enlighten me
almost forgot the car drives great and the gear box is really smooth

thanks for any help much appreciated