How do you program a new key for a 2005 scion tc?

To program a new key for a 2005 Scion tC, you'll need to have the new key and an existing master key. Insert the master key into the ignition and turn it to the "On" position for a few seconds, then back to "Off." Remove the master key and insert the new key, turning it to the "On" position for about 10 seconds. Afterward, turn it back to "Off," and your new key should be programmed and ready to use. If you don't have a master key, it's best to consult a dealership or a locksmith.