Why is the security light flashing and the engine will not start?
Short answer: A flashing security light usually means the immobilizer did not recognize the key, caused by a faulty key, a weak fob battery, a bad antenna or reader, a module communication fault, or lost synchronization between modules.
The immobilizer checks the key before allowing fuel and spark. If the key is not recognized, the engine may crank and stall or not crank at all, and the security light flashes or stays on.
Try a second key. If the spare works, the original key is likely damaged or its chip has failed. For smart keys, try the backup start method in the owner's manual, which usually involves holding the fob against a marked spot. If that works, the fob battery or the vehicle's interior antennas may be the issue.
If no key works, scan the immobilizer, engine and body modules for codes. Look for communication faults, antenna or reader circuit codes and low voltage. A weak battery can cause key recognition problems on its own. Repairs may involve the antenna ring, wiring, or reprogramming keys and synchronizing modules with a capable tool.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.