Key / Immobilizer Warning Light
The key or immobilizer warning indicates that the vehicle may not be recognizing the key correctly or that the anti-theft system has detected a fault.
Try the spare key if available and replace the key-fob battery if needed. If the engine will not start or the warning persists, diagnose the immobilizer system.
An immobilizer system prevents unauthorized engine starting by verifying the key or transponder. B2799 is commonly associated with immobilizer/key recognition on some vehicles, but exact definitions vary by manufacturer.
⚠️ Drive With Caution
If the engine is already running normally, drive only as necessary. If the immobilizer prevents starting, arrange diagnosis rather than repeatedly attempting to start the vehicle.
$20-$800+ depending on the key, programming, antenna, or module
Repair costs vary depending on the exact diagnostic trouble code, vehicle make and model, labor rates, and which component has failed. Always diagnose the problem before replacing any parts.
A key or immobilizer warning can range from a weak key battery to a vehicle security-system fault. Try the spare key first, then scan and diagnose the system if the problem persists.
Why does my car crank but not start with the key light on?
The immobilizer has not recognised the transponder in your key, so it is blocking the fuel or ignition. The starter still turns because that circuit is separate from the anti-theft block.
Will a weak key fob battery stop the car starting?
On push-button systems, often yes. Most of those vehicles have a backup position, usually holding the fob against the start button or a marked spot on the column, that reads the chip without battery power.
How is an immobilizer warning diagnosed?
Try the spare key first, since a working spare points straight at the original key rather than the car. Fit a fresh fob battery, confirm the vehicle battery is holding proper voltage, then scan the immobilizer or body module and check the ring antenna around the ignition barrel and its wiring.
How much does immobilizer repair cost?
A fob battery is a few dollars. A cut and programmed replacement key is usually $150-$450, and an antenna or control-module repair can reach $800.
See every fault code, sensor test, and repair step for B2799