There is an engine management system in the engine compartment that can recognize the signals transmitted from the key. If the correct signals are not detected the engine will not start.
The transponder receives the signal and then transmits its electronic code, by means of special frequency modulatons, to the control device which is able to process the code. The transponder has no external input power supply (passive system) – it receives the energy necessary to work from the signal emitted by the external control device (inductive coupling between the control device antenna and that of the transponder).
Depending on the system, the vehicle is automatically unlocked when the door handle, trunk release, or an exterior button is pressed. Vehicles with a smart key system fitted are required to have a mechanical backup, usually in the form of a spare key blade supplied with the vehicle. Some manufacturers hide the backup lock behind a cover for styling.
These changes/advances, which although good for crime statistics, pose challenges for vehicle owners and locksmiths/technicians involved in diagnostics. Most vehicle keys are fitted with a transponder (chip see picture below) which is a small electronic device that will fit into the head of the key or onto the circuit board of the central locking remote control.
This transponder (chip) holds a code which is transmitted to the vehicle’s immobiliser and if correct will allow the vehicle to be started and to continue running. Transponder technology has developed very rapidly and later systems are use rolling (cryptographic) codes to improve their security on later model vehicles. All work associated with transponders/immobilisers was originally retained within the car dealerships.
However, after market equipment is currently available to qualified/ licensed locksmiths, which allows cloning/copying of transponders and complete programming into the vehicle security systems.
Once the key is inserted in the ignition, the transponder is energised and sends a fixed code to the security module.
When the key is inserted into the ignition the transponder is energised and sends a rolling/changing code to the security module. Once the key is removed, the transponder sends a second code which will have rolled/changed to a different new code. The vehicle then will have the new calculation or code already stored in its memory ready for use the next time the ignition is turned on.
This type of system is in place to prevent easy duplication/coping of these keys. Later rolling code systems are also able to store more information, such as vehicle identification number (VIN) data to further protect the transponder chip encryption.
This means they do not require constant electricity and thus, they do not need a power source of their own. (No battery needed for power) Transponders operate in the frequency range area of 125 kHz. Since Magnetic Coupled Transponders do not have their own power source they are very limited to their range of communication.
Generally they operate in the range of 1 cm to 15 cm of the vehicles ignition system. Since this is a radio frequency, it can penetrate materials that would make the transponder not directly visible, such as the in the plastic head or rubber part of the key.
Once a key is inserted into the ignition lock and turned to one of the ‘on’ or ‘run’ positions, the induction coil that is mounted around the ignition lock (see diagram above) sends out an electromagnetic field of energy. The windings in the transponder chip (see picture below) absorb that energy and power the electronic chip to emit a signal.
The signal is usually an alphanumeric set of digits (hexadecimal) which is considered the Identification Code. The induction coil reads the signal. If the signal is recognised as being already in the computer’s memory, the signal is accepted and other electronic components in the vehicle are set into motion. This allows the starting of the vehicle and or the continuation of the engine running.