The idea of using any key fob for any car is a common misconception. Many car owners wonder if they can simply reprogram a spare or used key fob to work with their vehicle, especially with the rising costs of replacement keys from dealerships. The simple answer is generally no, you cannot program just any key fob to any car, particularly when it comes to starting the engine. Let’s delve into the reasons why and explore the complexities of key fob programming.
When considering key fobs, it’s crucial to understand that modern car keys are not just simple mechanical devices. They are sophisticated electronic components deeply integrated with your car’s security system. The primary function of a key fob is no longer just unlocking doors; it’s also about authenticating the key to allow the car to start, a system known as the immobilizer.
For starting your car, the key fob typically interacts with an immobilizer system, like BMW’s EWS (Electronic Immobilizer System). This system is designed to prevent theft by ensuring that only authorized keys can start the vehicle. Each car has a unique Vehicle Identification Number (VIN), and the immobilizer system is intrinsically linked to this VIN. Key fobs are programmed with specific encrypted information, often including an Individual Serial Number (ISN) that matches the car’s unique security profile. This encryption is VIN-specific, meaning a key programmed for one car will not be recognized by another car’s immobilizer system. Only the car manufacturer, or authorized dealerships, possess the database and tools to generate these VIN-specific key codes. Therefore, a used key fob from another vehicle, even the same make and model, cannot typically be reprogrammed to start your car due to this fundamental security measure.
However, there’s a separate aspect of key fob functionality: remote central locking and alarm systems (like BMW’s FZV and DWA). These systems operate independently from the immobilizer. In some cases, particularly with older vehicle models, it might be possible to program a used or different key fob to control the door locks and alarm system of your car. This is contingent on the key fobs operating on the same radio frequency as your car’s receiver (common frequencies are 315 MHz in North America and 433 MHz in Europe). Even if the frequency matches, successful programming for remote functions is not guaranteed across all makes and models and may still require specific programming procedures or tools. It’s important to remember that even if you manage to program a different key fob to lock and unlock your doors, it will likely still fail to start the engine if it’s not correctly programmed to the immobilizer system.
The technological reason behind this limitation lies in the transponder chip embedded within the key fob. In many systems, including older BMW E-series keys, this transponder chip is a “write-once” chip. This means that once it’s programmed with a specific ISN and linked to a VIN, this data cannot be overwritten or changed. Even with aftermarket software and hardware capable of extracting the ISN from your car’s computer modules (like the DME and EWS in BMWs), you would still need a blank, programmable transponder chip to write this data to. In many modern key fobs, the transponder chip is soldered directly to the circuit board, making replacement or reprogramming of the chip itself extremely difficult, if not impossible, for non-authorized individuals.
In conclusion, while the idea of universal key fob programmability is appealing, the reality is that due to sophisticated immobilizer systems and VIN-specific encryption, you generally cannot program just any key fob to start any car. While remote locking and alarm functions might offer some limited programmability in certain situations, the core function of starting your vehicle remains tightly controlled by security systems that require keys specifically programmed for your car’s unique identity. For replacement keys that start your car, especially for systems like BMW’s EWS, typically you will need to obtain a new key from an authorized dealership to ensure proper programming and functionality.
