I have a 2001 Grand Prix 3.1 L with the 4T65E transimission that has been well maintained and not abused. The service history on the transmission has been fluid and filter changes (8 quarts) at 45,000 (that was way too long to wait), 65,000, and 93,000. At about 90,000 miles (Oct 08), the transmission experienced the first P1811 hard shift in traffic after traveling on the highway before the incident at 70-80 MPH on a 80 degree day. The usual temporary solution of shutting the engine off and restarting after 5 minutes temporarily solved the problem.
I have actively researched the issue over the past year and made some changes to the transmission to help improve and then eventually solve the problem. The reason for the post is to alert some of you that this issue can be resolved on a 4T65E transmission that is essentially functioning correctly, been well maintained, and does NOT have other internal problems. I have noticed in my research that many recommendations surround replacing the PCS solenoids, TCC solenoids, worn second gear clutch, all the way to most of the time, transmission replacement for ridiculous dollars (BTW-gmpartsdirect sells brand new 4T65E transmissions for $1,300).
From what I have read, the 4T65E's do not like heat and since the transmission acted up when hot, the obvious solution was to add the biggest baddest double stack transmission cooler that I could fit in the grill which I did (28,000 GVW) after the radiator cooling. This change greatly minimized the problem but it still occurred occassional on hot days. The next step was to totally have the transmission be cooled by the tranny cooler, by passing the radiator completely. BTW-There is no problem in the cold other than it takes about twice as long to get over 77 degrees for lockup.
The final solution was the ZZ performance shift kit for $30 that speeds up the shifts in the accumulator (easy to do if you can change your transmission fluid and filter) since the hard shifts occur due to shifts occurring too slow (over .65 seconds) and the computer tells the transmission to go to max line pressure since it thinks that there is something wrong due to the slow shifts. Obviously, with 100,000 miles on the transmission, parts get worn but there is still plenty of life in a well maintained transmission with the hard shift occurring because the springs in the accumulator becoming weak with age and mileage allowing slower shifts, some clutch wear that needs to be compensated with the shift kit (there is no adjustment for the 2nd gear clutch), and/or a bad solenoid (s) that again can be compensated with speeding up the shifts manually with the shift kit.
The tranny cooler and shift kit cost about $100 and now has 4,000 miles on it and has not acted up once since I installed the shift kit which does not make the shifts harsh (choose the milder spacer setting), just speeds the shifts up. The transmission shifts perfectly now under all conditions.
My point here is that many people are spending big dollars to fix a relatively minor problem as long as the rest of the transmission is in good working order. Recommendations by transmission places to replace the solenoids for $700-800 dollars only to have the problem occur again or to replace the whole transmission for $1,800-2,500 is criminal when the problem can essentially be addressed with a $30-60 shift kit.
I hope that this will help some of you with this problem.
