Central locking not working
Start by separating remote from system: if the key button does nothing but the driver's door key or the interior lock switch locks all doors, the fault is the remote or its receiver, not the locking. If one door is left behind while the others lock, it is that door's lock actuator or the wiring in the door hinge loom. If nothing responds at all, look at the fuse, the body control module and the supply before touching any door.
Urgency
Safe to drive, fix soon
Possible causes, most likely first
- Flat key fob battery or lost synchronisation
Remote range shrinks over weeks and then stops; the car still locks from the door switch. Fit a new CR2032/CR2025 and, if it still fails, carry out the resynchronisation procedure for the model (often: key in ignition, press lock within a few seconds). - Failed door lock actuator
One door does not lock or unlock with the rest and the motor can be heard labouring or clicking. Swap the connector or measure 12 V pulses at the actuator plug while a helper presses lock; voltage present but no movement means the actuator. - Broken wires in the door hinge loom
Intermittent faults on one door that change when the door is moved. Pull back the rubber boot between the A-pillar and the door and flex the harness; look for green corrosion and cracked insulation. - Blown fuse or faulty locking relay
No door responds and the interior lock switch is dead too. Check the fuse for the central locking or body module and listen for the relay click; a blown fuse that blows again means a shorted actuator. - Body control module or comfort module fault
Random locking, doors locking themselves while driving or a BCM that no longer sees the switch inputs. Read codes from the comfort/body module; water in the module from a blocked drain or leaking door membrane is a frequent cause. - Microswitch in the driver's door lock
On cars that use the lock position to arm or disarm, a worn microswitch means the car does not recognise the door as locked. Read the door status on the scan tool while operating the lock by hand. - Weak car battery
Locking sounds sluggish and sometimes only half completes with a weak crank in the morning. Check battery voltage before chasing the locking system.
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What you can check yourself
- Replace the key fob battery and try the spare key
- Lock the car with the key in the door or the interior switch and note which doors respond
- Listen at each door for a motor sound when locking; silence on one door points to that actuator
- Check the central locking fuse in the fuse box