Transponder Key Programming

A transponder is a small chip in the head of the key with no battery of its own. When the key is near the ignition, a coil around the barrel energises the chip, the chip answers with a code, and the car's immobiliser decides whether to allow fuel and spark. If it does not like the answer, the starter still works — which is why the car cranks convincingly and then dies.

That distinction is diagnostically useful. A car that does not crank at all has an electrical or starting fault. A car that cranks strongly and refuses to fire, with a security light flashing on the dashboard, is usually telling you about the key.

Signs it is the transponder

• The engine cranks normally but never catches.
• A security or immobiliser light flashes or stays lit on the dash while cranking.
• A spare key starts the car and the usual key does not — that isolates the fault to the key.
• The problem began after the key was dropped, soaked, or had its case replaced.
• A key bought online or cut at a kiosk turns the ignition but will not start the vehicle — it was never programmed.

Have this ready

• Year, make and model.
• Every key you own, working or not.
• Whether the dash shows a security light, and whether it flashes or stays on.
• Whether the car has been jump started or had its battery disconnected recently.
• Proof of ownership.

Common questions

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