2000 Century trans hard shift and whine

2000 Century 103,000 miles, trans sometimes has hard shift and whine that I assume is the transmission. The whine increases with increased speed. Trans has not been serviced for the past 40-45,000 miles, but a fluid check shows it over full. Engine oil changes are done by a Buick dealer, but they have never mentioned the overfull trans fluid level, so I don't trust them to ask their advice on this problem.
The problem is intermitent but frequent.

Thanks for any suggestions.

You have the symptoms of a bad pressure control solenoid (PCS). The whining and hard shifting is caused by its inability to properly control line pressure. Best thing to do is get it scanned with a scanner capable of reading extended codes to see if a P1811 (Maximum Adapt & Long Shift) DTC is stored. The DTC will disable shift adapts and commands maximum line pressure. This causes the hard shifts and whining sound.

Thanks for the quick reply. Is the PCS expensive or difficult to install? Where is it located?

Not exactly a DIY bolt on job. Located under the side cover assembly. See pic below. Tranny shops like AAMCO/Cottmans wil charge approximately $550 or so for part and labor.

http://i5.photobucket.com/albums/y186/lizzywiz/valvebody2.jpg
EPC=PCS 4T65E Autotransaxle

Thanks for the quick reply. Is the PCS expensive or difficult to install? Where is it located?
Had the same symptoms you describe with my 2000 Century at 50K miles. Buick dealership replaced my PCS for $600, lasted about 13 months, just out of warranty, and started the harsh shifting and whine again. Since I drive 90% highway miles, I decided to live with it. Now at 200K miles I still have the intermittant shift problem however tranny still working otherwise.

Had the same symptoms you describe with my 2000 Century at 50K miles. Buick dealership replaced my PCS for $600, lasted about 13 months, just out of warranty, and started the harsh shifting and whine again. Since I drive 90% highway miles, I decided to live with it. Now at 200K miles I still have the intermittant shift problem however tranny still working otherwise.

That is a common problem to get the harsh shifting and whining back even after a PCS replacement. GM revised the PCS solenoid and portions of the valve body on 2003 and up GM cars with the 4T65E autotransaxle. But the part(s) cannot be retrofitted.

Most of the time all you have to do is turn ignition off for a few minutes then restart and the problem will disappear for awhile. Very intermittent. That is because the DTC that sets P1811 is cleared. Maximum adapt/long shift. When P1811 sets it disables shift adapts and commands high tranny line pressure which causes the shifting problem and whining sound.

Some people claim that either Seafoam or Lubegard tranny additive helps while the problem persists.

Thats what my Buick Century 2000 was doing and the shop replaced the bad pressure control solenoid (PCS). and that took care of the problem. cant tell you what it cost cause it was under waranty.