EB II V8 Gearbox.
Strange one here, at least to me. My '92 V8 EB II Fairmont S/W has developed an annoying tendency of dropping into self protect/limp home/stuck in 3rd gear mode when slowing down and dropping from 2nd gear back to 1st. It will sometimes cause a slight bump which can be heard and felt as it goes into 1st, but more often than not nothing unusual happens to indicate a change of mode has occured. The car has been standing for about 6 months, engine out, torque converter out and gearbox suspended at a slight forward facing downward angle. The gearbox sump pan was removed, oil filter, pan gasket and oil renewed. My local transmission magicians have had the car on their diagnosis unit shortly after the second occurrance, when the battery required disconnecting for a period of time to effect a reset and return to normal operation mode. Their diagnosis was "valve pressure solonoid circuit", and 1 "undefined code", however, they were unable to duplicate the problem in order to confirm the diagnosis and effect a repair. Since they have returned the car, a simple shut off the ignition and restart has reset the 'box. The only "real" attempt to to sort the problem has been the disconnecting of all the electrical plugs and spraying out with contact cleaner to eliminate moisture. The vehicle battery has been renewed, the previous battery being 5+ years old (but still seemed OK).
Any thoughts would be welcomed, from sticking/u/s solonoids to insulation breakdown on the wiring. The car has 297,000 kilometers on the clock.