People are regularly handed a key that fits the lock perfectly and does nothing. That is not a faulty key — it is an unprogrammed one, and the difference is worth understanding before you pay anybody.
The immobiliser, in plain terms
Since the late 1990s almost every car has an immobiliser: a small challenge-and-response system between the key and the car. Turn the ignition or press start, and the car asks the chip in your key a question. Right answer, the engine runs. Wrong answer or no answer, fuel and ignition stay cut.
This is why car theft by hot-wiring largely died out. It is also why key replacement stopped being a locksmith-with-a-file job and became an electronics job.
Cutting and programming are two separate things
Cutting shapes the metal so the blade turns the lock. Programming writes the key’s chip into the car’s list of accepted keys.
You need both. A cut-only key opens the door and turns the ignition but will not start the engine. A programmed key with the wrong cut will start the car once you are in, but will not unlock the door.
What can be programmed
- Transponder keys
- Remote head keys
- Push-to-start proximity fobs
- Additional spares alongside an existing working key
- Replacement fobs after water damage or a failed battery
What can go wrong
Cheap aftermarket fobs. Some simply refuse to pair, and no amount of equipment fixes a bad chip. If you bought one online we will test it and tell you before charging for the attempt.
Wrong sub-model. The same car in the same year can take two different fobs depending on trim. A fob that is nearly right is entirely useless.
Flat vehicle battery. Programming needs stable voltage. A car that has been sitting for weeks may need charging first.
Deleting old keys
On most vehicles, programming can also remove keys from the accepted list. Worth doing whenever a key is lost, or when you buy a used car and cannot account for how many copies exist. See car key programming for what we handle.
Where to go next
Need a locksmith in St. Louis? Call (314) 916-6766. Open daily 5:30am–11:30pm. Price agreed on site before any work starts.
Common questions
Why does my new key turn but not start the car?
It has been cut but not programmed. The immobiliser does not recognise the chip, so the engine stays disabled.
Can every key be programmed on site?
The overwhelming majority, yes, with the equipment in the van. A small number of makes and model years need extra steps and we tell you up front.
Can you program a fob I bought myself?
Often, but not always – quality and sub-model matter. We check it before charging you.
Can old keys be deleted?
On most vehicles yes, which is what you want after a lost key or a used-car purchase.