A keyless entry system is a complex amalgam of radio transmitters, electric motors and batteries, as well as touch screens in the high-end key fobs. Given the myriad of components that make up this system, problems and glitches are only to be expected. However, they can each be tested to make sure that the system as a whole works. This will require some disassembling of the key fob with a screwdriver, but the rest can be done with a few button pushes.
Walk toward the car with the key fob in hand. If the car has a proximity activated entry system, then the door will pop open assuming that no other parts are broken. If the car does not have this system, then press the open button on the fob to see if the door opens. If it doesn't, then the battery may be dead or the transmitter broken.
Press the open button on your backup key fob. If the door still does not open, then the receiver in the car is broken or one of your batteries is dead. Test the car battery by opening the car manually and trying to start the car. Replace the car battery if it is dead and try the open button again. Replace the key fob battery by removing the fob backplate and installing a new battery. Press the open button again to test the keyless entry system. If it still doesn't open, then the problem is in the receiver.
Unscrew the back of the key fob if the backup fob worked. There will be four Phillips headed screws located around the edges of the fob. Pull the back off the fob and locate the disc-shaped battery. Pull the battery out by hand and replace it with the same type of battery. Screw the back of the fob back on by hand with the screwdriver; do not use a power tool.
Press the open button again. If the fob still does not work, it will need to be replaced because a chip is blown or the transmitter is broken. Purchase a new fob at your dealership.
