The Lexus RX300 comes with a remote keyless entry system. If you need to reprogram the system, you can do it yourself. You'll need to determine which programming mode will work best for what you want to do. "Add" mode lets you add another remote. "Rewrite" mode will erase all stored remote information and add a new one. "Confirmation" mode tells you how many remotes are currently programmed. "Prohibition" mode will erase all remote information and disable the keyless entry system.
Open the driver's door and close all other car doors. Put the key in the ignition, then remove it.
Press the door lock switch to "Lock." Within one second, press it to "Unlock." Repeat this step until all the car doors have locked and unlocked five times.
Close the driver's door, then reopen it. Press the door lock switch to "Lock" again, then within one second press it to "Unlock." Repeat until the door locks have cycled five times again.
Put the key in the ignition and turn it to "On," then to "Off" within one second. Do this once to enter add mode, twice for rewrite mode, three times for confirmation mode and five times for prohibition mode. If you entered confirmation mode, the door locks will cycle once for every remote programmed. If you selected another mode, the locks will cycle the same number of times that you turned the key.
Press the "Lock" and "Unlock" buttons on the transmitter for 1.5 seconds. Release them and within three seconds, then press and hold any button on the transmitter for one second. The door locks will cycle once if you have done everything correctly. If you have not, the locks will cycle twice.
Close the driver's door to finish programming.