Additional Key cannot be Registered [08/2019 - ]: Description
WARNING: This page is about a different car, the 2022 Toyota Sequoia, 2021 Toyota Sequoia, and 2020 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.
If additional registration is not possible, a malfunction of the electrical key transmitter sub-assembly, certification ECU (smart key ECU assembly), engine switch, No. 2 indoor electrical key antenna assembly (front floor), steering lock ECU (upper steering column with switch bracket assembly) or door control receiver is suspected.