What is the security system/what does it do?

Modern cars have sophisticated and complex security systems, designed to project the vehicle from theft. These systems are controlled by an ECU (electronic control unit) which is part of the car's computer system. The key components of the system include door locks, ignition lock, steering lock, alarm and immobiliser. Some security systems have additional features such as automatic window closure, deadlocks, fuel flap locks, central locking, remote unlocking, keyless entry and tracking.

Getting into the details of security systems

At the heart of the system, the ECU controls most elements of the vehicle's security including remote unlocking, central locking, engine immobilisation and the alarm. The components work together to ensure that the vehicle cannot be unlocked or started without the keys or remote present. Additionally, the system ensures that unauthorised attempts to unlock the vehicle activate the alarm to act as a deterrent and to notify others. When the car is locked the ECU also immobilises the engine, making it difficult to start via ‘hot wiring’ of the ignition barrel.

Most vehicles with central locking systems also have a mechanical override of the door lock system, allowing entry into the car using the key in any of the doors fitted with an external lock barrel. This is useful in the event of a flat battery, as it allows entry into the vehicle to release the bonnet so access to the battery can be achieved.

Internally there may be various controls that interact with the security and locking system including individual door lock levers, central locking control, boot and fuel flap release mechanisms and alarm deactivation controls. These allow the occupants to lock and unlock the vehicle from inside the cabin.

One of the most complex parts of the security system is the central locking mechanism. This is largely due to the number of ways that the system can be controlled. As a result there are large number of interconnected components working with the ECU to control the door locks. The main components are lock barrels, lock mechanism, levers and switches, connecting rods, clips, actuators, motors and the electronics, including the ECU.

What if something goes wrong with the security system?

Door lock mechanisms can fail due to wear and tear of mechanical components or failure of the electronics. This can be as a result of corrosion, broken or damaged wiring, blown fuses or faulty electronic components, including switches, actuators or the central control unit (ECU).

Alarm and immobilisers systems are susceptible to electrical issues, damaged transponders or remotes, including loss of synchronisation with the car's ECU.

Other issues can occur due to attempted theft including forced or damaged lock barrels.