Both BMW Keys Stopped Working – What's Wrong and How to Fix?

BMW is a brand that most people opt for because of the luxury, classiness, and safety the vehicles offer the driver and the passengers. BMW has for many decades been receiving accolades for being extra reliable. But there are instances you might find yourself unlucky with your Bimmer. The car keys can stop working.

No-start problems highlights

• Level of urgency:high
• DIY inspection:possible but complicated
• DIY repair:impossible
• Can you drive?no
• Price for repairs:$200 - $450
• Symptoms:engine won't crank, light may or may not go on
• Ways to solve:check the battery, check the key fob, find a good mechanic

Understanding the BMW keys

All BMW cars are sold with two keys. The extra key serves as a spare and also lets an additional driver have access. Whether you have the first generation, the diamond-shaped, or the modern fob key, the seller should hand over an extra key.

In the old generation keys, BMW used a chip in the keys that acted as a security feature. Even though the physical key could be inserted in the ignition slot, the car wouldn't start if the chip malfunctioned. The now more common fob key won't have a physical key to insert in the ignition. All you have to do to start the engine is press the start/stop button, provided the fob is with you.

Several conditions must be met for the BMW keys to keep working as designed. Immobilizers, fuses, fuel systems, and alarm systems must be in working order for the car to start. However, like every other machine or system, the BMW engine can fail to start. Your Bimmer might even lock you outside because of a key malfunction.

Rarely will both your car keys fail at the same time. But some malfunctions and conditions can arise, which can make both the keys fail to unlock/lock and even start your car. When your car keys stop working, it is always advisable to start looking for the problem whose solution will cost you the least. For example, avoid assuming the engine is the problem whenever the vehicle won't start. The fault could be a dead fob key which will cost you $2.

Why are both BMW keys not working?

1) Blown fuse

If the car won't unlock even when you use the spare key, it is probably because the door lock fuses are blown. There are a number of fuses that ensure the door and window system works seamlessly. When any of these fuses blow, you will have a malfunctioning key.

Solution

Start by finding the fuse diagram of your car. For most BMWs, the diagram is located in a compartment inside the glove box. You will need to open the glove box and remove a plastic cover found on the wall of the compartment. You will find a paper drawing indicating how the car fuses are placed inside the fuse box, which is found right below the glove box compartment.

Look for fuses that have car doors drawn on them. The number of fuses varies from one model to the next and even from year to year. It is, therefore, important to look for the door diagram to get the right fuses. It is the cheapest solution because a set of fuses will cost you less than $5. If the fuses are working fine, it is time to check the fob battery.

2) Dead fob battery

The fob key comes with a battery. This battery powers the system inside the fob and communicates with the receiver inside the car. When the battery dies, the fob key will not send or receive signals from the car. Though rare, the batteries of both keys can die at the same time.

Solution

Modern BMW fob keys can either be sealed or openable. For the fob keys that are not sealed, you can easily access the inside with a tester or a screwdriver, or even your nails. The battery inside is a CR2032, and almost all major watch battery manufacturers have it. Sliding the old battery and inserting the new one should be easy.

As for the sealed fob keys, it is not impossible to go around a dead battery issue. Just buy a BMW fob key casing similar to your fob key on eBay or Amazon. Buy a CR2032 battery to replace the dead one. Break your fob taking care not to damage anything inside. The circuit board inside will easily come out together with the battery. Replace the battery and put the circuit board in the new fob casing.

Of course, this option is not popular with BMW dealerships because you have undercut them, but it is safe since you won't be interfering with the programming of the key.

3) Faulty diversity antenna

BMW cars, especially the newer models, have been equipped with a diversity antenna. This technology uses several antennas together to produce a better, clearer signal. This antenna in BMWs can be found on the back windshield and is also part of the window defrosting system.

BMW has put the radio antenna, the central locking antenna, and the brake lights wiring all in a single circuit board. Any damage to the board will make your key not work, especially on locking and unlocking the doors.

This technology has been embraced in many sectors, including mobile phones, to help improve the reliability of antennas and transmitters. In the BMW, the diversity antenna will fail either because of corrosion on metal parts of the board, blown fuses, or damaged wiring.

Solution

Like in our argument earlier, it is wise and cheaper to first check the items that will cost you the least amount of money. Start by checking the two 15amp fuses and confirm they aren't the ones causing the problem. You can then move on to check the circuit board wiring before deciding to buy a new diversity antenna. Secondhand diversity should cost anything between $50 and $200.

4) The central locking system wiring

The central locking system connects the diversity antenna with the central mirror, the battery, the fuses, and even the immobilizer. All these connections are done through wires. As you may be aware, wires, especially in vehicles, are prone to corrosion or getting cut. Once you have diagnosed all of the above probable causes and none seems to sort out the problem, check the wiring system.

Solution

Checking the wiring of the system is not easy or cheap. You will need the services of an expert. They will check any wire disconnection or corrosion for the entire vehicle. They will check the looming and sturdiness of the connections to the different circuit boards.

5) Key is deactivated

This is another possibility though rare. The previous owner of your Bimmer might have deactivated the second key, probably because they had forgotten to reactivate it. One can deactivate the 2nd fob key when they misplace it and want to avoid it falling into the wrong hands. They might have found the key later and forgotten to reactivate it before selling off the car.

Solution

We are assuming that your daily-use key has stopped working, and when you try the spare key, the car won't respond either. Before concluding that the spare fob is deactivated, you should first perform the above diagnostic tests. Check whether the battery is working fine and then the diversity antenna.

Reactivating your BMW fob key requires an expert in the coding field. The same process will be followed as if you had bought a new key. The BMW dealership will synch the key with the vehicle, and you will be good to go. For it to reach here, the fob key you have been using must have been declared spoilt first, and the only option for you is to replace it.

6) Immobilizer is faulty

The immobilizer is a critical component in your vehicle's central locking and ignition systems. The immobilizer ensures that your BMW can only start if the right key is used. It is common to fault the key whenever the car fails to unlock or start. However, the immobilizers have been known to malfunction. It is advisable to check the immobilizer, as you have confirmed the keys are working fine.

Solution

The most viable solution to a malfunctioning immobilizer is to replace it. A new immobilizer requires coding and locking it to your car. It is not possible to buy an aftermarket immobilizer as every BMW has an immobilizer specifically matched to it from BMW. The cost of a new immobilizer is high even though certain BMW mechanics claim they can repair it if not completely damaged.

Conclusion

If both keys to your BMW stop working, deductive reasoning is the best way to solve the issue. In most cases, the problem is as simple as replacing a fob key. In other instances, the problem can be huge, costly, and very frustrating. But in the end, you will get to the correct answer by following these simple steps.