Perhaps Prius ownership should be designated BK and SK, in the same manner years used to be designated BC and AD. BK is for all Gen II Prius models with black key fobs. SK is for those Prius models equipped with Smart Key System (SKS) functions. BK owners take heart: eBay and the Internet have made DIY fob replacement a reality. It's a two-step process: one sequence to turn on the Prius; a second to operate the doors.
Insert the current fob into the dashboard slot, then remove it. Repeat this sequence three more times for a total of four "in/out" sequences. Insert the fob a fifth time and leave it inserted.
Open and close the driver's door a total of six times.
Remove the old fob from the slot. The Prius is now in fob programming mode.
Insert the new fob and let it remain in the slot. Watch the blinking red light on the dashboard. When the light stops blinking and goes out, the new fob is programmed.
Remove the new fob. Test both fobs to ensure they work properly.
Open the unlocked Prius driver's door. (It doesn't matter if the other doors are unlocked or not.)
Insert and remove the present fob into the dashboard slot twice within five seconds.
Close and open the driver's door twice, then remove the old fob.
Insert and remove the old fob again once.
Close and open the driver's door twice again.
Insert the old fob in the slot, get in the Prius, and close the driver's door.
Press the power button without pressing the brake pedal, wait a second, press the power button again, wait another second, and press the power button a third time to turn the car off. Wait a second, press the power button yet again, wait a second, press it once more to again turn the car off.
Open the door, exit the Prius, and remove the old fob from the slot. The "add mode" is now engaged. (The Prius should automatically lock and unlock the doors twice to verify "add mode" is activated.)
Press both buttons on new the fob simultaneously and hold both down for a second and a half. Within three seconds of releasing the buttons, press just the lock button. The Prius should respond by locking/unlocking the doors. This verifies that the new fob is working.
Exit the programming mode by opening the door or putting a fob in the slot.