...okay you must check the dipstick level hot and with the engine running...it should be in between the two hash marks...check the color (should be cherry red) and the smell (should not have a burnt smell)...if the level is down look at the transmission coolant lines to the radiator...if all these things are okay would stop blaming the transmission and would look to the engine~
if any of these things are off, bring it to a transmission shop...they'll change the transmission filter drain the converter and change the fluid~
Is there more than 30,000 on the car? Have you ever serviced the trans? I would recommend that you have the trans flushed and serviced first so see if the problem go away first. Buick's have a know problems with the shift solenoids inside the tranny, sometimes a service will clean them up and will start to work properly. If they still act up then the side cover will have to be removed and the solenoids replaced.
Mine had this issue code I got was for the aiight solenoid had the filter chambers's and new oil put in it's OK but it still feels kinda rough tht may b ur issue
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