# Immobiliser light on or flashing: what it means and what to do _Updated: 8 November 2026_ **Short answer:** The immobiliser light looks like a car with a key inside, and when it flashes while the car is locked, that is normal: the protection is on. If it stays on or flashes after you turn the key and the engine won't start, the car does not recognise the key, so try the spare key. > **The service we recommend: Diagnostics** We read faults from every computer in the car and tell you what is urgent. We tell you the price when you tell us the model. [More about the service](https://autoindustrija.rs/en/services/car-diagnostics) ## Symptoms: when the light is normal, and when it is not The immobiliser is protection that stops the engine from starting without the right key. The key has a small chip with a code, and the car checks that code every time you turn the key or press the start button. The light shows what the car has decided. [More about what an immobiliser is](https://autoindustrija.rs/en/advice/what-is-an-immobiliser) - **Flashes while the car is locked and switched off:** Normal. The protection is on, and the light flashes until you start the car with the right key. - **Comes on for about 3 seconds when you turn the key, then goes out:** Normal. The car has recognised the key and the engine can start. - **Stays on or flashes, and the engine will not start:** The car does not recognise the key, so it cuts the fuel, the starter or the ignition. - **The engine starts and dies straight away:** This can also be the immobiliser: the car has not recognised the key, or the parts of the immobiliser are not exchanging a signal. - **Car with a start button: the light flashes and the key is in the car:** The car cannot find the key. A common cause is a weak battery in the key. ## What to do when the light is on and the engine will not start 1. Take the key out of the ignition, or on a car with a start button switch the car off with the button. Then try again. 2. Take other chip keys and metal fobs off the key ring, and move your phone away from the key. 3. Do not leave the key on the dashboard or in the glovebox. On a car with a start button, press the start button with the key itself. 4. Try the spare key. If it starts the car, the fault is in the first key. Stop after 3 tries. Turning the key for a long time can cause a new fault. If the spare key doesn't start it either, the fault is in the car, and the car stores such a fault. [More about when the car won't start because of the immobiliser](https://autoindustrija.rs/en/advice/car-wont-start-immobiliser) ## Why the car does not recognise the key: common causes - **Another chip key or metal next to the key:** Metal and another chip interfere with the signal between the key and the car, so the car cannot read the code. - **The key is where the signal is hard to pick up:** On the dashboard or in the glovebox the car struggles to pick up the key signal. A phone can also interfere with it. - **A weak battery in the key, on a car with a start button:** The key signal gets weaker. Another sign is that the central locking does not work from the remote. Until the battery is replaced, start the car by pressing the start button with the key. [More about when keyless does not work](https://autoindustrija.rs/en/advice/keyless-entry-not-working) - **A damaged chip in the key:** Moisture, static electricity and knocks can damage the chip in the key. We then make a new key and program it into the car. [More about the car locksmith](https://autoindustrija.rs/en/services/car-locksmith) - **A key that is not programmed into this car:** The car does not recognise its chip's code, so the engine will not start. - **A fault in the car:** The key is not to blame, but the immobiliser or a part it exchanges data with. We find this fault with diagnostics. **Whether the key battery affects the immobiliser depends on the key** - **A key you turn in the lock:** no, the chip needs no battery, the car reads it when you turn the key. - **A car with a start button:** yes, a weak battery weakens the key signal. ## When the fault is not in the key The immobiliser exchanges data with the engine computer, and on some cars with the instrument cluster as well. So the fault does not have to be in the key. It can be in the cluster, in the computer or in the link between them. When the instrument cluster is replaced, the immobiliser is set up again with a diagnostic device. When the immobiliser is repaired, the keys are programmed again. So bring all the keys you have to the check. We find and repair electrical faults. [More about the auto electrician](https://autoindustrija.rs/en/services/auto-electrician) ## The light flashes or stays on while driving The light flashes or stays on while you drive? Do not switch the engine off, because it may not start again. Drive straight to a check. [More about car diagnostics](https://autoindustrija.rs/en/services/car-diagnostics) On a car with a start button, the light can flash at any time when there is a fault in the key system. Then too, bring the car in for a check soon, before the day it does not start. ## The “Immobilizer active” message on the dashboard Some cars show the message “Immobiliser active” or “Immobilizer active” instead of a light. It means the same: the car has not recognised the key. Take the key out and try again. If the message appears even with the right key, the immobiliser is faulty and should be checked straight away. With diagnostics we find where the fault is. ## Does the factory immobiliser protect against theft? It protects against hot-wiring under the steering wheel, but not against a thief who makes a new key through the OBD port. From then on the immobiliser treats that key as genuine. The add-on immobiliser we fit also needs your small fob: without it the engine will not start, whichever key is in the car. [More about the add-on immobiliser](https://autoindustrija.rs/en/services/immobiliser) ## Frequently asked questions ### The car started on the second try. Should it be checked? If it happened once, look at what was next to the key: another key, a metal fob or a phone. If the car fails to recognise the key again, bring it in so we can check the key and the immobiliser. ### What if I have lost a key? We make a new key and program it into the car. At the same time we delete the lost key from the car, so whoever finds it cannot start the engine. [More about key programming](https://autoindustrija.rs/en/advice/car-key-programming) Have a question about your car? Message us on WhatsApp or call 067 774 1606. ## Read also - [Car dashboard warning lights: meaning and when to stop](https://autoindustrija.rs/en/advice/dashboard-warning-lights) - [Check engine light (engine warning light): what it means and what to do](https://autoindustrija.rs/en/advice/check-engine-light) - [Car won't start: what to check first](https://autoindustrija.rs/en/advice/car-wont-start) --- Page on the website: https://autoindustrija.rs/en/advice/immobiliser-warning-light auto-industrija, Belgrade. Phone and WhatsApp: +381677741606. E-mail: kontakt@autoindustrija.rs.