January 01st, 2015 - Transponder Keys

Fig. 1 Texas Instruments 4C Transponder

Fig. 2 Ford H-72 Transponder Key

Automotive security has made significant advancement in recent years. Transponder systems have greatly increased the security of our vehicles. Transponders are small transceivers that are hidden in the bow of the key.

These transponders are truly remarkable little devices. They transmit a unique digital signature that the ECU (Engine Control Unit) of the vehicle recognizes and thus allows the vehicle to start. If a key that is not programmed to the ECU, or a force tool is used to turn the ignition, the car has an immobilizer unit that will prevent the engine from starting. Immobilizers and transponders have made these vehicles less attractive to thieves.

The transponder has no power of it's own. There is an antenna coil around the ignition lock cylinder. As soon as the key is turned to the "on" position, the antenna coil transmits an electromagnetic signal that energizes the transponder inside the key, and it in turn transmits it's unique number back to the antenna coil. When the ECU recognizes the key, it allows the car to start.

See Fig. 1 for an example of a transponder. You can see the electronics in one end of the capsule. You can see the antenna coil in the other end, which both receives the electromagnetic signal from the antenna coil around the lock cylinder, and transmits the signal back to same.

See Fig. 2 for a view of the same transponder imbedded into the bow of the key. This particular key is made with clear plastic so you can see what is going on inside the key.

Older cars, and some newer cars that are not transponder equipped, have a code series that is specific to that model. A code series dictates how many different keys are used when the cars are manufactured. A particular code series will usually contain 1,000-10,000 different keys. In other words, if a code series contains 1,000 different codes, there will be 1,000 different keys that are utilized as the cars roll off the assembly line. So, after 1,000 cars roll off the line, they start over and every 1,000th car shares the same key.  Car #1 shares the same key as the car #1,001,  #2,001 etc. etc.

Transponder equipped vehicles share these same code series as their low-security counterparts, but the transponder adds a superior level of security. Along with the few thousand possible mechanical keys, the transponder's transmitted electronic code has in excess of a billion different possibilities, rendering it virtually unique. So even if a thief were able to manipulate the mechanical portion of the lock or force the ignition to the start position, the immobilizer would still prevent the car from starting.

At Automotive Lock-Works, we specialize in servicing both transponder and non-transponder equipped systems. Feel free to call me with any questions you might have about automotive locksmithing.

Taylor Miller
(479) 422-3115