Transponder Key

The chip needs no battery: it is powered by the antenna around the ignition lock. Remote buttons and keyless entry use a separate battery. Each new or replacement key has to be programmed to the car, usually with dealer or specialist equipment. The chip in a transponder key usually needs no battery; it is powered by the reader’s antenna when the key is close.

Transponder keys are different from the remote control buttons that lock the doors. The remote needs a battery and works from a distance; the transponder chip works only at close range and controls whether the engine may start. A key with a flat remote battery can therefore often still start the car.

When you turn the key or press start, the antenna energises the chip and reads its code. The immobilizer compares it with stored codes. Many systems use rolling or encrypted codes, so the car and key exchange a different code at each start.

A damaged chip or unprogrammed key causes a no-start with the security light on. Keep the spare key safe: it is the quickest way to rule out a key fault. Losing all keys can be expensive, because new keys must be programmed to the car. Keep a spare key in a safe place.