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Immobilizer: working principle

Immobilizer: when your car won’t start

Immobilizer: foolproof system?

As its name indicates, the immobilizer blocks the starting of a vehicle in the absence of authentication of the start key. Let’s see how it works in more detail.

Immobilizer: operating principle

In the absence of authentication, the system acts as a switch and blocks the power and ignition functions (for gasoline engines) of the engine management computer.

It consists of:

• keys or cards (2);
• a transponder integrated with each key, which will communicate with the vehicle;
• an immobilizer control box: this is the electronic switch that will authorize the power and ignition functions (it can be integrated into the main control box (BSI);
• A transponder coil is an interface between the immobilizer and the transponder in the key: the antenna allows communication with the transponder.

When the key or card is detected (remotely, key inserted in the lock, or key in the ignition switch, depending on the system), the immobilizer checks the presence of the transponder and emits a random code.

The authorization to unlock the car is given when the key, through the transponder, sends back an authentication code. This recognition is possible because the immobilizer and the keys are trained in the factory, which matches them.

Immobilizer: when your car won’t start

• Theft of a key or card: relearning the existing key (with a new duplicate) is necessary to deactivate the stolen key. Different cases may arise:
• The loss of keys or cards requires the reprogramming of the keys at the dealer.
• If your vehicle does not start: in this case, you must try the spare key.
• If the car starts: it is your key that is at fault. Check the battery, and if it is not at fault, it is the integrated electronics that are deficient. The solution is to replace the key and relearn it.
• If the vehicle still does not start: it is an internal vehicle component (immobilizer – transponder coil – engine management computer, etc.). The transponder coil can be checked and replaced without difficulty. The immobilizer (external or internal to the cabin computer) or the engine management computer requires reprogramming by the dealer.

Warning: with some manufacturers, if your key no longer works following a change of plastic shell, you have probably left the transponder in the old cover!

Immobilizer: infallible system?

The immobilizer is a safe system, mandatory on new vehicles since 1998. However, it is not infallible; moreover, its neutralization is possible, and the imagination of the manufacturers to make their system reliable is only equaled by that of the crooks to counter them.

There is no question here of providing more in-depth information on the flaws in these systems, as some sites, unfortunately, do this without any qualms.

If he does not start the vehicle in a few minutes, the thief usually does not insist on his work. To discourage potential thieves, insurance companies often require an additional anti-theft system. Even better, if you have some knowledge of electricity, you can install start-up disabling systems yourself, which are very effective because they are customized.

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