Warning lights
Key or immobilizer light: the car does not recognize the key
When the car does not recognize the key, the immobilizer stops it from starting or lets the engine run for just a couple of seconds, and a key-shaped light or a message usually appears. The most common cause is the key fob battery or a low car battery.
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Is it serious? Can I keep driving?
Usually not urgent, but do not ignore it. It is not dangerous: the car simply will not start or keep running. If the warning appears while the engine is running, do not switch it off until you reach a safe place, because it may not start again.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Dead key fob battery: the most frequent cause on keyless cars; the key is no longer detected at a distance.
- Low car battery: with little voltage, the immobilizer and the key reader can fail.
- Damaged or unprogrammed key: a knock or a failed chip; a new key has to be programmed to the car.
- Key antenna or reader: the coil around the ignition or the antennas of the keyless system.
- Communication between control units: if the immobilizer unit cannot talk to the engine unit, it will not allow the start.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: How can you tell if the 12 V battery is failing? What do U codes and lost communication (U0100) mean?
Car system: Electrical system and battery
What you can check yourself
Try the spare key: if the car starts, the problem is the first key.
On keyless cars, hold the key at the spot the owner's manual shows (often near the steering column) so it can be read even with a weak battery.
Replace the key fob battery with the same type.
Check whether the rest of the car works normally: dim lights point to the battery.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0513Incorrect immobilizer key: malfunction
- P0633Immobilizer key: not programmed - ECM/PCM
- U0167Lost communication with vehicle immobilizer control module
- P0562System voltage: too low
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: immobilizer and engine codes, communication with the immobilizer unit and battery voltage.
Frequently asked questions
How long does a key fob battery last?
It depends on the key and how it is used. Having to get closer to unlock the car is the first sign it is running low.
Can I program a new key myself?
Usually not: it takes a tool and, for many makes, protected access from the manufacturer. A shop or a specialist locksmith does it.
Why does it start and die after two seconds?
That is typical immobilizer behavior when it does not recognize the key: it lets the engine fire and then cuts it.
Keep reading
- Electrical system and battery: how it works and what fails
- Car will not start and does nothing or just clicks
- Engine cranks but will not start: causes and what to do
- Car will not start with a new battery: what it could be
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means