My 04 TL has 103k and recently acting up so weird.One day while driving check engine light,vsa and triangle light were on.I was on sport shift mode doing 70 mph and it automaticcally down shift to 4 and lock it there ,can not down shift or up shift.Pull over turn off engine then turn on and drive for like 15 mim local street then same problem happen again but this time im lock in 2nd gear by the way my car is 5AT.I thought my tranny was fucked. bring it to shop scan it and found this code DTC P2138.
APP SENSOR
ACCELERATION PEDAL POSITION MALFUNTIONED.

 

dang so many tranny problems with 3g TL's. good luck man!

 

https://acurazine.com/forums/showthr...&highlight=app

https://acurazine.com/forums/showthr...&highlight=app

 

Fortunately, the error code for OP's car showed an Accelerator Pedal Position sensor failure and not a transmission issue.