Either the transmission is overfilled or the transmission vent is plugged.
IF you have over filled the transmission this will cause it to bubble, this could cause serious damage, drain and refill with the proper ammount.
If too much transmission fluid is added, or there is something wrong with the pump
dipstick o ring missing,wore out or dipstick is not in good
The same thing that causes soda to bubble when it is poured on almost anything.
why does oil come out of dipstick on a1996 12v commin
If the fluid is full of bubbles or is foamy, the transmission is probably overfilled with ATF. Other causes include using the wrong type of ATF or a plugged transmission vent. REF: http://www.aa1car.com/library/atf.htm
Assuming it is an automatic transmission, I would check the fluid level. When the transmission is warmed up, the level should read 'full' on the transmission dipstick. Check the color and smell of the oil. Does it smell burnt, or does it appear to be brown instead of red? Perhaps the filter screen is clogged.
sounds to me like it is too full. some trans. have to be checked in nuetral with engine running. it usually gives instructions on the dipstick
Excessive crankcase pressure will cause this problem two possible causes are worn/broken piston rings or a blocked engine breather.
The answer is not pleasant. There is none. GM saw fit to save a few dollars and not include them. The owners manual says that if transmission trouble is suspected to return the vehicle to a dealership where they have a tube and dipstick and will check the fluid level ( no doubt at a small fee). The only problem is that by the time the low fluid causes symptoms it is usually too late.
It is possible it is one of the speed sensors.
When was the last time you serviced the Transmission. Pull out the dipstick on the transmission while car is running with the transmission in park. and check the fulid level is it full of fluid?, if so smell the fluid does it stink or look dark? Then this may be all you need to do is take it to a Shop and let then service it for you.