In a few words:
The immobilizer or anti-theft system verifies that the key used to turn the engine on is the correct one. If the key is not the correct one, this system blocks different actions to prevent the car from starting.
When this system is activated, a warning light will turn on on the dashboard or instrument panel. Here are some examples:
If the car does not recognize the signal of the key, two things may happen:
The car's computer will disable the fuel pump, the ignition coil and/or the injectors, depending on the electronic immobilizer system. Moreover, if the car has a diesel engine, this system will also block the “stop” relay, which will prevent the fuel from being injected into the engine. Sometimes, this system will also block the steering column which will lock the steering wheel.
The main reason is because the car's computer does not recognize or does not detect the signal sent by the chip which is inside the key. The most common reasons as to why this happens are:
⚠️ Low battery of the key or the remote control: the chip will not send the signal.
⚠️ The chip of the key is damaged or has been decoded: it may happen if the key is damaged or if it gets wet.
⚠️ Faulty electrical wiring: it may happen both in the antenna as well as in the immobilizer unit or the engine's computer.
Less frequent causes:
Since this system is delicate, it is advisable to leave this process in the hands of a specialist.
First, the technician will scan the car with the adequate diagnosis equipment to check if the problem is actually related to the immobilizer system.
If that is the case, the technician will have to identify the cause among the causes already mentioned and then see if this problem can be solved via programming or if it is necessary to replace any of the components.
Each original key has a chip inside which sends a signal when it gets close to the ignition switch. Inside the switch there is an antenna which receives this signal and sends it to the car's computer. If the signal is the same as the one the car has saved, then the driver will be allowed to start the car.
The immobilizer is automatic and manual activation is never needed. Remember that you can check if your car has this system or not in your owner's manual.