If your car battery dies, the car computer's memory will be erased, including the authorisation of your working remote-entry fobs. You'll need to reprogram the computer to recognise them again. If you simply bought a new fob, you'll have to program all the fobs in one session. If you can get your hands on the instructions to do the programming yourself, it can save you upwards of £65 in service charges at your local dealership. Unfortunately, programming instructions are numerous. For instance, Chevrolet has at least 16 sets of instructions for its cars, and none of them work in place of the others.
Check your owner's manual for the remote programming instructions. If the manufacturer didn't include them, go to Step 2. If you don't have a manual, try ownersmanualsource.com or diplodocs.com, which provide car manuals for free.
Open programyourremote.com. This site has remote programming instructions for almost three dozen makes. Instructions are broken down by make, model and model year. Navigation of the site is self-explanatory. Try a similar model/model year if you can't find one that precisely matches yours. Otherwise, proceed to Step 3.
Call a dealership to get instructions for free over the phone. This is a last resort. Target out-of-town dealers, since they won't lose remote-programming business by giving you the instructions.
If the above strategies don't work and you want to find instructions by doing an Internet search, you can narrow your search by focusing on the keywords "fob" or "keyless," "program" and the car model.
Some cars have no owner-friendly programming instructions, requiring special equipment at the dealership. Hyundai, Mercedes and several Buick models have this problem.