The Ultimate Car Key and Immobiliser FAQ

In this article we will answer in detail all the main questions that concern car keys and immobilisers.

How to Check if Your Car Key Contains a Chip (Transponder)

A simple method to check this is by using aluminium foil. Take a piece (e.g., from a chocolate bar) and tightly wrap the entire body of the key in several layers, leaving only the blade exposed. Make sure no part of the key’s casing is visible.

Now try to start your vehicle:

• If the engine fails to start or starts and then stalls, your key likely contains a transponder chip, and your vehicle is equipped with an immobiliser.
• If the engine starts and runs normally, your vehicle may not have an immobiliser system, or it is deactivated, and the key likely contains no chip.

How to Identify the Type of Chip in Your Key

Check the Catalogue: The easiest (but not always accurate) way is to look up your key in a transponder chip catalogue or ask us directly via the “Ask a Question” form at the top of the page.

Open the Key: Carefully open the key casing and inspect the chip for markings. Send us a photo of the chip’s inscription, and we’ll help you identify it.

For example, NXP (formerly Philips) chips are typically marked with identifiers like PCF7931, PCF7935, PCF7936, PCF7937, or PCF7938.

Some integrated RF module chips may only have an internal manufacturer code or no marking at all.

Call an Auto Locksmith: If you’re unable to disassemble the key, visit a professional auto locksmith. Even with basic equipment, they can usually identify the chip type by attempting to read or copy it.

Key Fob Frequency Ranges

Keyless entry remotes operate on different frequencies depending on the region:

• North America (USA, Canada): 315 MHz
• Europe, Russia, and many other countries: 433–434 MHz or 868 MHz
• Japan: 300–315 MHz

Vehicles imported from other regions may use non-standard frequencies, so always check the key or RF module for the frequency marking.

Is It Necessary to Program a New Key to the Vehicle?

Yes, pairing is mandatory. Without pairing, an immobiliser would not protect the vehicle from theft. Only select manufacturers (e.g., BMW, Mercedes, Land Rover) allow remote key ordering through official dealers with full documentation. Any other key—original or aftermarket—must be manually programmed.

Programming involves:

1. Transponder chip (for starting the engine)
2. Remote control buttons (for locking/unlocking doors)

Can a Used (aftermarket) Key Be Programmed?

It depends on the chip type and vehicle manufacturer.

Older keys with fixed-code chips can often be reused multiple times (e.g., early systems or Toyota’s pre-programmed keys).

Some chips store unique vehicle data after the first pairing, and unless they allow password rewriting, they cannot be reused with another vehicle.

Most modern chips use encryption and password protection. Without knowing the old password, you cannot reprogram the key.

However, central locking buttons (remote control) can often be reused even if the chip cannot. In some cases, you can replace the chip and blade while reusing the original RF circuit board.

How to Program a Transponder Chip

For transponder programming, it’s best to contact a specialist in vehicle immobiliser systems or an authorised dealership. Immobiliser specialists have advanced tools that can:

1. Pre-program blank keys
2. Write directly to memory (EEPROM dump)
3. Work around dealer restrictions

Dealerships, however, can only perform functions permitted by the manufacturer.

How to Program Central Locking Buttons

In many cases, remote buttons can be paired manually by following a sequence of steps (e.g., turning the ignition key and pressing buttons in a certain order). These procedures are often consistent across models of the same brand and generation. You can easily find them online with a quick search.

How to Make a Duplicate Car Key

Visit a local locksmith or key-cutting service:

1. They can cut the key blade and clone the chip (if possible).
2. To save on cost, you may buy a key shell, blank blade, and transponder chip in advance, and bring them to the workshop just for cutting and cloning.

Copy vs Pairing a New Key: What’s the Difference?

Copying involves making a full duplicate of an existing chip. The vehicle recognises the duplicate as the original. However:

• Modern chips have non-rewritable serial numbers.
• Fixed-code chips (e.g., PCF7935) are the exception and can be copied.

Pairing (Programming) involves registering a new chip using OEM tools or professional equipment. This is necessary when cloning isn’t possible due to encryption or security measures.

Which Chip Emulator Should I Use for Copying?

Choose an emulator that:

• Supports the chip type you want to copy.
• Is compatible with the cloning device you plan to use.
• Popular chip emulators include TPX, CN, and JMD series.

Which Car Chips Can Be Cloned?

As of early 2017, the following chips are commonly cloneable:

1. Fixed-code chips: ID11, ID12, ID13, 4C, ID44
2. Rolling code chips: 4D (40 80-bit), ID46, and some ID48

Manufacturers frequently update their encryption methods, so compatibility may vary with time.

What Is a “Blank” or “Prepared” Chip?

These terms refer to new or pre-initialised chips intended for use with standard key programming procedures. After manufacturing, chips contain default values (e.g., passwords, identifiers, operational settings).

Some manufacturers pre-load their own data into chips before pairing to:

1. Set the chip into the correct operational mode
2. Ensure only their branded keys can be paired

In such cases, the vehicle will validate this data before allowing the key to be registered.

Car Key Pairing Methods

Factory Method using a dealer scanner or diagnostic tool.

EEPROM Programming by writing directly to the immobiliser’s memory.

Cloning an existing transponder.

What Is a Chip Emulator?

A chip emulator functions like a standard transponder but allows:

• Multiple rewrites of the ID and data pages
• Flexible configuration

Use in remote start systems or advanced car key duplication

Can I Cut a Key Blade Using the VIN?

Yes, but only if you have access to the manufacturer’s database, which links VINs to cutting codes. In some cases, the key code may also be found:

1. On the original key
2. On the ignition lock
3. In the vehicle’s service booklet

Can You Order a Car Key Using the VIN?

For certain brands (e.g., BMW, Mercedes, Land Rover), authorised dealers can provide a fully functional key using just the VIN—provided all paperwork and proof of ownership is in order.

Types of Car Key Chips

ID13 – Fixed code embedded during manufacturing. Not rewritable. Can be cloned to a T5 chip.

4C – Manufactured by Texas Instruments (TI). Fixed code, non-rewritable. Can be cloned to emulators like TPX1, TPX2, CN1, CN2, and JMD-4D.

PCF7935 – Made by NXP. Rewritable chip with password protection capability. Can be cloned to another PCF7935.

PCF7936 – Produced by NXP. A rewritable HITAG2 chip with encryption and write-protection. Can be cloned to TPX4, TPX5, CN3, and JMD46.

PCF7941, 7945, 7946, 7961 – Similar to the PCF7936 but with an integrated RF (remote control) module. The PCF7961 (also known as PCF7922) features a fully integrated RF module.

4D (40-bit) – From Texas Instruments. Rewritable with DST40 encryption. Data can be write-protected. The encryption key can be changed without knowing the original key. Uses challenge-response authentication. Can be cloned to TPX2, CN2, or JMD4D.

4D (80-bit) – Also by Texas Instruments. Enhanced DST80 encryption with greater data capacity and same write-protection features. Can be cloned to CN5 or JMD-G.

ID48 – Rewritable and encrypted. Can be cloned to a JMD48 emulator.

How to Identify HITAG2 Chips by Their ID

NXP HITAG2 series chips each have a unique identifier. The second-to-last digit of the ID often indicates the chip type (part number). See the example table below:

Can I Make a Chip for Remote Start Using a Smart Key?

Yes. Most smart keys can be used to create a chip for remote start. This is possible because smart keys often replicate the functionality of a standard transponder key.

If I Buy a Key with a Chip, Will It Need to Be Programmed?

Yes. If you purchase a complete key with a chip or remote buttons, it must be programmed (paired) to your car and the blade needs to be cut.

You’ll need to visit an immobiliser specialist for programming. The key blade can be cut at a key service or locksmith.

If you’re only buying a replacement key shell (housing), no programming is needed—just cut the blade and transfer the internal components from your old key.

Does a 4C Chip Already Contain a Code, or Is It Blank?

A 4C chip always contains a factory-programmed code. It is not blank and cannot be rewritten—only read.

To make the car accept the chip, its code must be present in the immobiliser’s memory. This can be done by either writing the chip code directly into the immobiliser or using the vehicle’s standard key learning procedure.

Why Is the Chip Type Important When Buying a HITAG2 (ID46) Key?

NXP offers a wide range of chips supporting the HITAG2 encryption protocol. The most common and basic one is the PCF7936, which includes the full HITAG2 feature set.

The PCF7937EA includes additional user memory where the car may store data.

For keys with remote buttons, NXP produces chips like PCF7941, PCF7945, PCF7946, and PCF7947, combining HITAG2 with a controller and a small amount of user memory. Without power, they behave like a basic PCF7936. Once powered, the internal controller activates, and the manufacturer’s code runs to control the remote buttons.

Later, NXP introduced newer chips like PCF7961 and PCF7922 to replace the above. These offer increased memory and a built-in RF transmitter, enabling the entire key to be made using a single chip.

What Should I Consider When Choosing a Car Key?

In many cases, the first 4 bits of the last byte in the chip ID specify the chip type. Some vehicles (especially Vauxhall) check this value before allowing a key to be paired. So, it’s important not just to match the chip functionality, but also to ensure the identifier and remote control firmware match what the car expects.

Have questions or need professional help with car key replacement and programming? Give us a call — Phoenix Car Keys is here to assist you with fast, expert service.