A car key programmer is a device that can be used to recode the transponder in a mechanical key or key fob. Some modern automobiles have specially coded transponders in their keys and will not start or run if the proper signal is not received. In some cases a new key can be programmed without any special equipment, though many vehicles require a device referred to as a key programmer. A key programmer may be a standalone unit, though they are sometimes integrated into complex scan tools. Key programmers typically bidirectionally interface with the on-board diagnostics II (OBD-II) connector.
When a key for a modern automobile is replaced, the new unit will often turn the mechanical switch but fail to initialize the system or start the vehicle. If this occurs, it is typically because the transponder inside the key has not been coded to that particular system. Keys can often be obtained from either the dealership or a locksmith, though they need to be coded regardless of the source. Some vehicles allow the owner to code their own key, which typically requires the presence of one of their original keys. This process differs between vehicles, though it usually involves placing the original key in the ignition, pressing a special combination of the brake and gas pedals, and then replacing the original key with the new, uncoded one.
If a vehicle does not have a self programming feature, a key programmer will typically be required to do the job. These programmer units are usually bidirectional OBD-II tools that connect to the same location as other scan tools. Many vehicle manufacturers sell units that specifically program keys for their vehicles, though generic units that handle a variety of makes and models may also be found.
The process of using a key programmer typically involves plugging the tool into the OBD-II interface so that it can communicate with the vehicle. Each programmer tool has different options and procedures, though they typically allow the operator to pull the programming data from the computer and then recode the transponder and computer to work with each other. After the key programmer has been used, the new key should function just like the old one.
Some vehicles use key fobs instead of traditional lock and tumbler keys. In some cases the fob only has to be in close proximity to the vehicle to work, while other cars require that it be inserted into the dash. Key programmers can be used with these fobs in many cases, and the process is typically similar to that used with regular keys.