Two problems related to transmission solenoid have been reported for the 2001 Acura TL. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2001 Acura TL based on all problems reported for the 2001 TL.
Transmission slips between 3 and 4. Doesn't do this all the time, however; many, many forums are full of 2001 Acura Tl's having transmission solenoid issues. We bought car used (163,000), many cars out there with the exact same issue which should have been addressed in the 2000's.
First noticed the failure after parking the car and then putting it into reverse to back out of the parking lot. Proceeded to drive normally, put the car in d5 (automatic mode) and noticed hard abrupt shifts from 1st gear to 2nd gear. 3rd gear seemed like neutral, car just revved and then caught 4th or 5th gear. Once in high gear and up to around 60mph on the highway the car suddenly downshifts to what seemed like 1st gear causing the tires to lock up for about a second and then went back into 5th gear. Fortunately there was no one behind me following to closely. Continued to drive, only slower this time and it did it again at about 45 mph this time. I pulled over and called the local dealership(Acura of baton rouge, la) and had the car dropped off for repairs. Solenoid replacement didn't solve the problem so he informed me that they would replace it with a remanufactured transmission. Car would be ready in about a week and a half.