MY 2000 BUICK CENTURY PERFORMS LIKE A DREAM. EXCEPT OCCASIONALLY IT SHIFTS VERY HARD (JERKS THE CAR) IN THE LOWER TWO GEARS. THERE DOESN’T SEEM TO BE A PATTERN. ONE SPECIALTY SHOP SAID A CODE CAME UP ON DIAGNOSTIC THAT INDICATED THAT THE TRANSMISSION WAS BAD, WOULD NEED REPLACING, AND WOULD LEAVE ME STRANDED IF I DIDN’T GET IT FIXED, LIKE, RIGHT NOW. WE TOOK IT ANOTHER SPECIALTY SHOP WITHOUT A FANCY DIAGNOSTIC COMPUTER, BUT YEARS OF EXPERIENCE. THEY DROVE & DROVE IT, BUT IT NEVER ACTED UP. THEY ALSO SAID, TRANSMISSIONS DIDN’T GO OUT SUDDENLY & WE WOULD HAVE WARNINGS. A THIRD MECHANIC, AGAIN, YEARS OF EXPERIENCE, SAID IT COULD BE THE VACUUM. WHAT SHOULD WE DO? WE WANT TO KEEP THIS CAR TO PASS ON TO YOUNGER FAMILY MEMBERS IN A YEAR OR SO. IT GETS GREAT MILEAGE, AND IT IS IN EXCELLENT CONDITION (WE BOUGHT IT NEW). WE DON’T WANT TO BE STRANDED EITHER, OR INCUR MORE DAMAGE IF IT QUITS OUTRIGHT. THANK YOU.
Please get your caps-lock key checked out. Could be a bad acumulator or cracked valve body. At any rate it’s just going to get worse. Chances are that you will need a rebuild sooner rather than later.
(In online terms, all capital letters means yelling).
I will just add to that - there isn’t a diagnostic code that tells you that a transmission is bad. There is obviously a problem, and the code is telling you about it. But it doesn’t tell anyone what to do.
It is also the case that transmissions can go out suddenly - though complete and sudden death is less likely than having it go into “limp mode” which usually sticks it in (I think) 2nd gear. The limp mode is largely a protective mode - if the computer detects a problem serious enough it will do this to help keep you from doing further damage.
Anyway…occasional hard shifting can have a lot of causes - try to find out what the actual diagnostic codes from the first shop were and put those codes up here.