A transponder key is essentially a key with a code transmitter embedded that sends a unique alphanumeric code to your ignition. When received, the transponder in the ignition tells the car that it is OK to start. Programming or reprogramming a transponder key depends on the make and model of your vehicle. For domestic cars with a vehicle identification number (VIN) that starts with 1 or 4, the keys can be reprogrammed by simply taking the keys out to your car and entering the program mode.
Enter your vehicle and put the key into the ignition and turn it to the "ON" position. Leave it in for 10 minutes and 30 seconds.
Before 45 seconds pass, turn the key to the "OFF" position. Then turn it back to the "ON" position. Wait another 10 minutes and 30 seconds.
Repeat the above step by turning the key to the "OFF" position within 45 seconds. Then turn it back into the "ON" position.
Turn key to the "OFF" position and then back to "ON." The key is now programmed. Turn it in the ignition to check.
If you have a domestic car that has a VIN that starts with a 2 or a 3, or if you have a foreign car, consult you owner's manual about programming the keys. If you are advised to take the issue to a dealership, consult an automotive locksmith instead. Find one that you located through a professional organisation such as the Associated Locksmiths of America.