Remote not working

Usually when you replace the battery, you gotta have it programmed to your car. Similar to how you have to pair a bluetooth headset with your cell phone for them to recognize each other and work together. Otherwise, any remote would unlock any car. Does that make sense? So either read up how to do it online, or the dealer will do it for a small fee.

Try this, http://my.is/forums/f53/01-05-lexus-is300-key-remote-program-instructions-407990/. This is detail instructions on how to program your key and remote.