Three separate things in one lump of plastic
- The blade. The shaped metal part. It turns the door lock and, on older cars, the ignition.
- The transponder chip. A tiny passive chip in the head of the key. It has no battery. When you turn the ignition, the car sends out a signal, the chip answers with a code, and the immobiliser decides whether to allow the engine to run.
- The remote. The buttons. This part does have a battery and talks to the car’s central locking over radio.
They can fail independently, which is why the symptoms matter so much when you phone.
What the symptoms tell you
- Buttons do nothing, key still starts the car. Remote problem — often just a battery or a worn button contact.
- Doors unlock, engine turns over but dies immediately. Classic immobiliser rejection. The transponder is not being read or is not coded.
- Key will not turn in the barrel at all. Mechanical. Either the blade is worn or the lock is.
- Nothing at all, no lights. Check the car battery before you blame the key.
If a copy was cut at a hardware shop and the car will not start, nothing is broken. The blade was copied, the chip never was. It needs coding.
What “coding” actually involves
Coding means connecting to the vehicle and teaching it to accept a new chip, or teaching the chip to answer the way that specific car expects. It needs equipment that talks to the car’s immobiliser system, and it has to be done at the vehicle.
On many cars, adding a key is straightforward when a working key already exists. With no working key, the process is longer and on some models restricted to the dealer.
Proximity and push-start keys
Keyless systems have no blade to turn. The whole fob is programmed to the car, and there is normally an emergency blade hidden inside for the door. These are more expensive to replace, which makes a spare more worth having, not less.
The practical advice
Change the remote battery once every couple of years before it strands you. Keep the spare somewhere other than the same keyring as the original. And if you only have one key for a car you rely on, get a second one cut and coded while the first one still works.
Need this sorted rather than explained? Nick is on 072 481 3352, or start a request with “Transponder / remote” already filled in.