Immobiliser Warning Light / Key Not Recognised

The immobiliser warning light (usually a car outline with a padlock, or a key symbol) indicates the immobiliser system isn't recognising the key. The car will not start while this warning is active — the immobiliser prevents the fuel injectors from operating without a verified key signal.

Common causes and fixes:

Flat key fob battery — the most common cause. The transponder in the key fob needs battery power to communicate with the car's receiver. Replace the key fob battery (CR2032 on most keys, £2–5 from any supermarket). If you're stranded, hold the key as close as possible to the start button or ignition barrel — sometimes the transponder can still communicate weakly enough to allow starting even with a flat battery.

Damaged key — physical damage to the key fob can break the transponder antenna. Replacement keys from a dealer or auto locksmith are required (£80–300 depending on vehicle).

Weak receiver in the car — the aerial that reads the key signal can fail. Usually requires dealer or specialist diagnosis.

ECU fault — if the ECU has been reset, replaced, or lost its key pairing data, the immobiliser can trigger. The keys need reprogramming to the ECU — a dealer job or a specialist with the correct software.

After a battery disconnect — some cars temporarily show the immobiliser light after the battery has been disconnected and reconnected. Starting the car normally clears it within 1–2 key cycles.

If you're locked out: Do not attempt to bypass the immobiliser — a reputable auto locksmith with the correct equipment can match new keys, and dealers can supply and program replacement key fobs.