CAR KEYSCan you program your own car key?

Situation one: the car has a built-in procedure

Some vehicles, mostly older ones, let an owner add a key with a built-in procedure, usually a set of steps with the ignition, the doors or the pedals. On a lot of cars the buttons and the chip are programmed separately, so getting the remote to lock the doors doesn't mean the key will start the car. It generally needs one or two keys that already work, and on several common makes it takes two, so it's no help if you're down to your last key. Not every car has one, and the steps are different for each make, model and year, so look up your exact vehicle instead of following a general video.

Situation two: the car needs a programmer

Many cars need a programming tool. It plugs into the OBD-II port under the dash, the same port a scan tool uses, and tells the car's immobilizer to accept the new key. Tools differ in which vehicles and functions they cover, and some features cost extra, so a tool that works on one car may do nothing on another.

Situation three: the car wants more than a programmer

Some makes, including a number of European brands and newer vehicles with protected networks, require security access before they'll accept a key. That can mean a PIN code, an online authorization from the manufacturer, or extra steps with the car's modules. It can call for dealer-level software or access that's only given to registered shops and locksmiths, and on some cars the key has to be ordered through the dealer with proof of ownership. It's the case where it's easiest to buy a tool that doesn't cover it, and sometimes the honest answer is that it isn't a do-it-yourself job.

Adding a key versus all keys lost

Adding a key when you still have a working one is usually the easy case. When every key is lost, there's no working key left to tell the car a new one should be trusted, so many vehicles need extra steps, sometimes including work on a module. If you have a spare, keep it somewhere safe.

Before you buy a key online

• The FCC ID and the part number on your original fob, if it has buttons. Two fobs can share an FCC ID and still not be interchangeable, so match both.
• The chip type the vehicle expects. A key with the wrong chip won't program.
• The blade profile, and whether the key arrives cut or uncut.
• Whether your vehicle can be done with a built-in procedure or needs a tool, and which tool.
• Whether the key is new or used. Many smart keys lock to the first car they're programmed to, and a used one may never program to yours.

A few ground rules

Only work on vehicles you own or have the owner's permission to work on. Follow the exact procedure for your year and model. Some cars have lockout timers or limits on how many keys they'll accept. Some procedures erase every key that isn't there when you run them, and a cheap tool or a weak car battery in the middle of programming can leave the car not starting at all. If the car is down to its last working key, that's the wrong time to experiment.

Not sure how the key and the car talk to each other? Start with what a transponder key is.