# Car key copying and programming

> Copies of keys with remote fob, a new key when all have been lost and keys that won't start the car. Transponder, remote fob, immobiliser and keyless keys.

- URL: https://www.reprogramacionesmbv.com/en/car-keys/
- Index for AI (llms.txt): https://www.reprogramacionesmbv.com/en/llms.txt
- Versión en español: https://www.reprogramacionesmbv.com/llaves/
- Reviewed: 2026-10-15

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Wanting a second key is not the same as having lost them all, and neither is having a key the car won't recognise. Each situation is solved in a different way. Find yours and we'll tell you what needs doing.

**In short:** A modern car key has three parts: the blade or mechanical part, the transponder (a chip the immobiliser has to recognise before it lets the engine start) and the remote fob that locks and unlocks the car. Making a new key is, above all, registering the transponder in the car's immobiliser. If you have a key that works, we start from it; if you've lost them all, the immobiliser data has to be accessed from the vehicle's control units. The price is on request, depending on the model and the type of key. We do it at our workshop in Alcalá de Henares or as a mobile service within the Community of Madrid.

## How a key with an immobiliser works

For many years now, turning the key or pressing the start button hasn't been enough to start the engine. The car first asks the key who it is:

**The three parts of a key**

- Blade or mechanical part: Opens the door by hand and, on cars with an ignition barrel, turns the ignition
- Transponder: A battery-free chip that the immobiliser reads by radio and has to recognise as its own
- Remote fob: A battery-powered transmitter that locks and unlocks; it is independent of starting

The **immobiliser** stores the list of authorised transponders. It may be in its own unit, in the engine ECU, in the comfort module or spread across several of them. A new key only works once its transponder is on that list. That's why "copying" a key isn't just making an identical one: it's teaching the car that it exists.

## I have one key and want another

This is the simplest situation. With a working key, the immobiliser can be accessed through the diagnostic port or by reading the unit where it's stored, and the new one added. The process, broadly speaking:

1. We check what type of transponder and remote your key has.
2. We prepare the new key with the correct transponder and frequency.
3. We register it in the immobiliser alongside the one you already have, and synchronise the remote.
4. We test both: starting, unlocking and locking.

**Tip**: if you only have one key left, don't wait until you lose it. Having a second one costs much less than solving an all-keys-lost case.

## I've lost all my keys

Here there's no key to start from, so the immobiliser data has to be reached another way. Depending on the car, that means reading the memory of the module that stores it (sometimes by removing it) so that new keys can be registered. It's a longer and more delicate job.

What you need to know:

- **The car can't be moved under its own power**, so we normally come to you. We explain it in [mobile service](https://www.reprogramacionesmbv.com/en/trade/mobile-service/).
- **Take the opportunity to make two keys**: that way you won't end up in this situation again.
- **The lost keys are left out**: when the new ones are registered, the old ones stop starting the car.

If the immobiliser module is also faulty, the job is combined with [BSI cloning](https://www.reprogramacionesmbv.com/en/bsi-cloning/) or [engine ECU cloning](https://www.reprogramacionesmbv.com/en/ecu-cloning/), depending on where the data is stored.

## The key exists, but it won't start the car or unlock it

Before making a new key, it's worth knowing whether the one you have can be saved:

| Symptom | Likely cause | What we do |
|---|---|---|
| Won't unlock remotely, but starts | Flat remote battery or remote out of sync | Battery replacement and, if needed, synchronisation |
| Unlocks, but won't start and the immobiliser warning light comes on | Damaged transponder or one that has come loose inside the casing | Transponder check; if it fails, a new key |
| No key will start the car | Immobiliser aerial, immobiliser module or engine ECU | [No-start solutions](https://www.reprogramacionesmbv.com/en/no-start-solutions/) and diagnostics |
| Works on and off | Broken casing, worn buttons, contacts | Casing replacement keeping the electronics |
| Keyless key isn't detected | Low battery or interference | Try with the key in the emergency position shown in the handbook |

If all the keys fail at once, it would be odd for them all to have broken on the same day: the problem is almost always in the car, not the keys.

## Keyless keys

On cars that unlock and start with the key in your pocket, the key communicates with several aerials spread around the car. That brings two particular points:

- **Programming is usually more demanding** and, on some makes, depends on modules with extra protections. With the make, model and year we'll tell you whether we can do it.
- **When the battery runs out**, the car almost always has an emergency spot (on the steering column, in the cup holder or under a cover) where you hold the key to start it. Check the handbook before giving the key up for lost.

## What we'll ask you for

To give you a price and a timescale we need:

- **Make, model and year** of the car, and whether it starts with a turning key or a button.
- **How many keys you have** and whether any of them work.
- **A photo of the key** (if you have one), both sides.
- **Where the car is**, in case we need to come to you.

To make a key we'll ask for the vehicle's **registration certificate (permiso de circulación)** and the **registered keeper's ID (DNI)**, or an authorisation from the registered keeper if that isn't you. It's how we make sure the key is for someone who is entitled to it.

The metal blade is not cut at our workshop: we take care of the transponder, the remote fob and the programming in the immobiliser.

## How much it costs

Key copying and programming is **price on request**. The price depends on:

- **The situation**: adding a key when you have another is the simplest; all keys lost, the most laborious.
- **The type of key**: with blade and remote, flip key or keyless.
- **Where the immobiliser is** in your car and how it has to be accessed.
- **Whether we come out** to the car.

We give you a fixed price before we start. You can ask for it using the [quote form](https://www.reprogramacionesmbv.com/en/quote/).

Tell us what's happened (you want another key, you've lost them or it won't start) and, if you have one, send us a photo of the key. We'll tell you how we'll sort it out.

## Frequently asked questions

### Can I buy the key online and have you just program it?

Sometimes, but there's a catch: the key has to have the transponder and remote frequency that match your model and your market, and some used keys can't be reprogrammed to another car. Before you buy it, send us the part number and we'll tell you whether it will work.

### Why does the remote unlock the car but it won't start?

Because they are two separate systems inside the same key. The remote works by radio and runs on the battery; starting depends on the transponder, which doesn't need a battery. If it unlocks but won't start, the problem is in the transponder, the immobiliser aerial or the immobiliser itself.

### I changed the battery in the remote and now it doesn't work. What should I do?

First check that the battery is the right type and is fitted correctly. On some cars the remote loses its synchronisation when it runs out of power and has to be synchronised again; the procedure depends on the model. If you can't manage it, get in touch.

### If one of my keys has been stolen, can it be cancelled?

On most systems, yes: when the keys are programmed, the one you no longer have can be left out so that it stops starting the car. It's best to do this as soon as possible.

### How long does it take to make a key?

It depends a lot on the situation and the model: adding a key when you have another isn't the same as rebuilding the system with all keys lost. With the make, model and year we'll give you an estimate when you book.