Cause
Damaged or worn key transponder
The chip inside the key damaged, so the immobiliser cannot identify it. The transponder has no battery — it is powered inductively by the antenna ring — so this is physical damage rather than a flat cell.
Keys get dropped, sat on, washed and carried on heavy rings, and the chip or its aerial loop cracks. The symptom is a vehicle that cranks and will not run, with the immobiliser warning showing. Trying the spare is the fastest test available: a second key that works proves the vehicle is fine and the first key is not, which is a five-second diagnosis that saves a great deal of work. A worn key that turns the barrel still says nothing about the chip — the mechanical and electronic halves fail independently.
Typically specialist work. Needs equipment or training most home workshops do not have.
Some of these codes mean you should stop driving
1 of the 1 codes this can cause indicate a fault where continuing to drive risks damage or is unsafe. Which one you have matters more than the cause does — read the code's own page before deciding.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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