Crash Bytes (Apr. '08)

The Latest Word on Transponders

By now just about everyone knows that a "transponder" is an electronic encoded device installed in the ignition key that allows the key to communicate with the ignition lock and the vehicle's electronic control module (ECM). The engine will start only if a proper code is recognized. What you may not know is that there are three basic types of transponders, one of which can be "defeated" under the proper conditions.

The three transponder types -- either fixed code, rolling code, or encrypted code -- differ only in the manner in which the key code is assigned. In a fixed code system, one unique code is assigned by the manufacturer to the transponder embedded in the key, and it never changes. With a rolling code system, the ECM randomly changes the code with each engine start and reprograms the key to the new code. An encrypted code system "scrambles" the code as it is transmitted back and forth between the key and the ECM, and the ECM changes the code with each engine start.

The rolling code and encrypted code transponder keys cannot be cloned. A duplicate key can only be obtained through the dealer from the manufacturer. However, a fixed code key can be duplicated -- by a properly trained expert using sophisticated (and very expensive) equipment.

There are two ways a thief can make a duplicate key for a fixed code system. First, using an aftermarket programming/servicing tool (available to independent locksmiths) he (or she) can defeat the steering column, gain access to the ignition switch, and energize the vehicle electronics. This takes some talent and training, because the transponder ring antenna encircling the ignition lock, must remain attached and undamaged, and the thief must have a new, non-programmed key for that specific vehicle present and in very close proximity to the ring antenna. Under these conditions, the programming tool will read the code stored in the ECM, will assign it to the new key, and the engine can be started with the new key.

A second method uses commercially available cloning equipment, and requires that the original transponder key be inserted in the device. The fixed code in the transponder is read and stored in memory. When a new, non-programmed key for that specific vehicle is inserted, the new transponder key is programmed with the code. The key can then be used to start the vehicle.