Central Locking and Keyless Entry

Central locking is an electrically actuated system that locks or unlocks all vehicle doors simultaneously from a single operation — the driver's door key cylinder, an interior lock switch, or a remote key (key fob) signal. The system uses a motor or solenoid actuator inside each door (and typically the boot/tailgate) to move the locking mechanism between locked and unlocked positions. The BCM coordinates these actuators, ensuring all lock simultaneously and monitoring door switch feedback to confirm successful operation. Remote keyless entry (RKE) extends central locking to radio-frequency remote control from outside the vehicle — the key fob transmits a coded 433MHz or 315MHz signal to the BCM-integrated or standalone receiver, triggering the lock/unlock function without physical key use. Passive Keyless Entry (PKE), also called Keyless Go or Smart Key, uses short-range radio frequency identification (RFID) or ultra-wideband (UWB) technology to detect an authorised key fob within proximity of the vehicle (typically 1–2 metres) and automatically unlock the doors when a door handle is touched, without any button press required. Combined with push-button start, PKE creates a completely keyless driving experience. PKE antenna placement around the vehicle allows directional detection of the key — approaching the driver's door unlocks the driver's door first; approaching the rear unlocks all doors after the front.

Central locking exists primarily for convenience and security — a single operation locks or unlocks all access points simultaneously, ensuring no door is accidentally left unlocked and reducing the time spent at the vehicle in vulnerable locations. The BCM typically enforces logic rules on the locking behaviour: the driver's door cannot be locked from outside with the key inside (to prevent lockout), the system may automatically lock all doors when the vehicle reaches a set speed (speed-based auto-locking), and the doors may unlock automatically when a collision is detected through the airbag module. Remote key systems use rolling code encryption to prevent replay attacks — each key press transmits a unique code that the vehicle's receiver validates against a synchronised counter, preventing an intercepted code from being used again. Key fob battery condition directly affects remote range — a weak battery reduces the signal strength and effective range significantly. The first sign of a failing key fob battery is typically a reduction in operating range from several metres to requiring close proximity to the vehicle.

Remote key reduced range or intermittent operation: The most common central locking fault. Replace the key fob battery (typically a CR2032 coin cell, available widely) before investigating any other cause. Battery replacement restores full range immediately if the battery was the cause.

Single door not locking or unlocking: An individual door actuator motor failure causes that door to remain in its current position when central locking is operated. The actuator can be tested by listening for the motor sound at the door during lock/unlock operation — a working actuator produces a brief electric motor noise; a failed actuator is silent. Actuator replacement requires door panel removal.

Passive keyless entry not recognising the key (or starting the engine): The antenna that detects the key's proximity may have failed, or the key fob may have been damaged or desynced from the vehicle. Replace the key fob battery first. If the vehicle still doesn't recognise the key, the key may need to be reprogrammed to the vehicle using dealer diagnostic tools.

Level 1 — Key Fob Battery Replacement: Replace key fob batteries proactively every 1–2 years, or immediately when remote range decreases. The battery type is usually printed inside the key fob case (most commonly CR2032). Keep a spare battery in the glove box. Most key fobs have an emergency mechanical key blade that can be used to enter the vehicle manually if the key fob fails completely — locate this and test it in the door lock before an emergency requires it.

Level 2 — Annual System Test: Test central locking from all available inputs (remote, interior switch, and mechanical key) annually to confirm all actuators are functioning. Test boot/tailgate locking separately. On vehicles with passive keyless entry, test the proximity range in a low-interference environment to confirm all door handle antennas are detecting the key correctly.

Level 3 — Professional Programming: Key fob programming to the vehicle (required after key loss, battery replacement on some platforms, or actuator BCM replacement) requires professional diagnostic equipment on most modern vehicles. Lost keys or additional keys require dealer-level programming tools that authenticate the key's electronic identity to the vehicle's immobiliser system.