How Do Transponder Car Keys Work?

How Do Transponder Car Keys Work?

lock in car

A transponder key is a car key with an inbuilt chip that is needed to deactivate an engine immobiliser. Most cars post-1995 have these immobilisers.

The engine control unit (ECU) of the car sends an electronic message to the key when the ignition is turned to on or run. The car will only start if it receives the correct message back from the key.

Transponder is the words “transmitter” and “responder” combined. The word emerged at around 1945. A transponder is a small electronic chip that has a “non-volatile memory” which doesn’t need constant electricity for data retention. A transponder also features a set of windings, or coil, which is made of fine wire wrapped around a tube. This is similar to the windings in an electric motor.

There are two kinds of transponders – electric coupled systems, and magnetic coupled systems. Electric coupled systems can transmit data anywhere from a few inches to many miles, such as those used in aeroplanes and satellites. They require significant amounts of constant energy to function. Magnetic coupled systems, in contrast, are passive – they do not need constant energy or a power source. They transmit and receive data on the 125kHz bandwidth. Because they are un-powered, they have a limited transmission range – anywhere from 1 to 15 centimetres. This radio transmission can penetrate certain materials such as the plastic surrounding the chip built into a car key.

How it Works

Most car transponder chips have a similar process for key identification. There is an induction coil mounted around the ignition lock. This generates an electromagnetic field when a key is inserted into the ignition and turned. The windings in the key absorb that energy and use it to power the transponder chip which then emits the code signal to the ECU. The signal is most often an alphanumeric code. This process allows the electronic components in the car to function which in turn allows the engine to start or continue running.

Transponder keys can be cut and programmed using our special equipment here at Out and About Locksmiths.