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What is an immobilizer and how does it work?

Almost always, in the configuration of a purchased new car, the line “regular immobilizer” appears, and used cars for the most part are not deprived of such a device. Moreover, many owners do not even know that it is in their car, since its operation is not noticeable during everyday use, For this, in this article, we will explain in detail the following points related to this system.

  • What is an immobilizer?
  • The working principle of the immobilizer system
  • What are the advantages and disadvantages of the immobilizer system?
  • Can the immobilizer device be replaced by the alarm device?

What is an immobilizer?

An immobilizer is an electronic anti-theft device, the function of which is to prevent the engine from starting and driving in the event of an attempted theft. Actually, the main function of the immobilizer is hidden in its name - from English the word immobilizer is translated as "immobilizer".

Structurally, immobilizers can be different - for example, some can open the car's electrical circuits responsible for ignition or fuel supply, while others can work via the CAN bus, programmatically blocking the engine start. However, functionally, all immobilizers have a single purpose: to ensure the impossibility of starting the engine and further independent movement of the car in case of theft.

In everyday use, the operation of the immobilizer is invisible to the car owner: as a rule, a key or key fob is used to unlock it, which, getting into the ignition switch or simply within the coil antenna of the immobilizer unit, turns off the immobilizer system and allows you to start the engine without hindrance.

The working principle of the immobilizer system

The operation of the immobilizer is organized as follows: when the ignition is turned on, the immobilizer unit briefly sends a high-frequency signal to the communication coil with the key chip and waits for the response code through the same coil. Through this high-frequency signal, power is supplied and communication with the chip in the key is carried out. In some systems, the immo also transmits a unique request code that tells the key chip that the reading is performed by a “native” car (almost all European and Japanese cars since 2000). In response, the chip sends its personal code. The received code is compared with the codes of the recorded keys in the immobilizer's memory, and if it matches, then a connection is established between the immobilizer and the engine control unit. Communication takes place digitally or via a K-line or via a CAN bus and is a request-response. The ECU sends 4 bytes of a random number to the immo, the immo encrypts these bytes in a certain way and sends 4 bytes of response back to the motor unit. If everything is correct, then the engine is allowed to start. If at any stage a failure occurs, the engine starts and immediately stalls. Both the operation of the fuel pump and the pulses to the injectors and the supply of sparks to the candles are interrupted. The prohibition of launch is at the program level.

What are the advantages and disadvantages of the immobilizer system?

The advantages of the immobilizer as an anti-theft device are obvious: it provides a certain level of protection against car theft, while often included in the list of standard equipment and does not require additional installation. The degree of protection depends on the type of immobilizer, as well as on the place of its installation: the easier it is to get to it by opening the car, the less potential protection against theft it provides. This, by the way, is the main disadvantage of standard immobilizers: they are convenient because the unlock chip is built into the standard key and does not require additional manipulations to start the engine, but the problem is that standard immobilizers are installed on the conveyor in a regular place, and the hijacker, knowing where the immobilizer is located in a particular model, can quickly “defuse” it.

Can the immobilizer device be replaced by the alarm device?

A specific answer cannot be given to it simply because the alarm and immobilizer are devices that are different in functionality. The alarm, as you know, serves to alert others and the car owner when trying to steal, attracting attention with light and sound signals and transmitting relevant information to the key fob. The immobilizer, on the other hand, does not notify anyone of an attempted theft, but only prevents its implementation, so the alarm and the immobilizer may not replace, but only complement each other.

It should be noted at the same time that most of the alarms have their own additional immobilizer, which is installed in pair with the regular one or, in its absence, as the main one. The advantage of this non-standard immobilizer is that, unlike the regular one, it can be placed in an unknown and hard-to-reach place for a hijacker.


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