# Car won't start because of the immobiliser: signs and what to do _Updated: 8 November 2026_ **Short answer:** If the dashboard lights up but the engine won't start and the key light flashes or stays on, the immobiliser does not recognise the key and blocks starting. Try the spare key: if that doesn't start it either, the fault is in the car. > **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) ## How to tell the immobiliser is to blame 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 immobiliser checks it every time you start the car. **What the immobiliser stops depends on the car** - **The starter:** the engine does not crank. - **Fuel or ignition:** the engine cranks but does not start. - **A dashboard light shaped like a key or a car with a key inside flashes or stays on:** The car has not recognised the key. - **The engine cranks and does not start, but the key light is not on:** Then the cause is often fuel, not the immobiliser. [More about what to do when the car won't start](https://autoindustrija.rs/en/advice/car-wont-start) - **The engine starts, then stops straight away:** The car may not recognise the key. The cause can be another chip key on the same key ring. - **Remote locking does not work either:** The key battery is probably flat, so the car does not receive its signal. - **It clicks rapidly when you turn the key:** That is more likely a flat battery than the immobiliser. [More about battery replacement](https://autoindustrija.rs/en/services/car-battery-replacement) ## What to do straight away 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. They interfere with the chip signal. 3. On cars with a start button, do not leave the key on the dashboard or in a compartment. Press the start button with the key itself. 4. On cars with a key ignition, hold the fob as close to the ignition as you can while you turn the key. 5. Try the spare key. If it starts the car, the fault is in the first key. If you are not close to home, ask someone to bring it to you. Stop after 3 tries. Turning the key for a long time can cause a new fault. ## What if the spare key does not start it either? Then the fault is not in the key but in the car: in the immobiliser, in the engine computer or in the link between them. With diagnostics we read the fault and find where it is. [More about car diagnostics](https://autoindustrija.rs/en/services/car-diagnostics) The immobiliser light flashes while you drive? Do not switch the engine off, drive straight to diagnostics. If you switch it off, the car may not start again. [More about the immobiliser light](https://autoindustrija.rs/en/advice/immobiliser-warning-light) ## When the key is to blame - **A key you turn in the ignition:** The chip in the key needs no battery. The car reads it when you turn the key. When the spare key starts the car and this one does not, we check the chip in this key. - **A key for a car with a start button:** A flat battery weakens the key signal and the car does not see it. [More about when keyless does not work](https://autoindustrija.rs/en/advice/keyless-entry-not-working) - **The key was dropped, got wet or is damaged:** The chip can fail from moisture, a knock or static electricity. 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 new key was only cut, not programmed into the car:** Such a key turns the lock but does not start the engine. ## A new key has to be programmed into the car When the chip is broken or the key is lost, we program a new key into the car through a computer. This is called key programming. We delete the keys you do not have from the car. A deleted key no longer starts the engine. Bring all the keys you have. A key that is not with the car while we delete the keys stops working afterwards. [More about key programming](https://autoindustrija.rs/en/advice/car-key-programming) ## How to switch off the immobiliser We do not switch off a factory immobiliser. Manufacturers warn that altering this system can cause an electrical fault, and then the car cannot be driven at all. The immobiliser is also theft protection: when a thief joins wires under the steering wheel, the immobiliser still does not let the fuel and the starter work. So we do not remove the protection, we find and fix the fault. [More about fixing electrical faults](https://autoindustrija.rs/en/services/auto-electrician) The factory immobiliser does not protect against a thief who makes a new key through the OBD port, the port diagnostics plugs into. 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 ### What if the add-on immobiliser fob goes flat? You unlock the engine with the backup code you get with the device. We show you how to enter the code after fitting. Carry the code with you or save it in your phone, and do not leave it in the car. When the device warns that the fob battery is low, replace it straight away. [More about the immobiliser](https://autoindustrija.rs/en/services/immobiliser) 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/car-wont-start-immobiliser auto-industrija, Belgrade. Phone and WhatsApp: +381677741606. E-mail: kontakt@autoindustrija.rs.