Replacing the battery in your 1999 Mercedes-Benz key fob is a straightforward task that can save you time and money compared to visiting a dealership. This guide will walk you through understanding your key fob system and how to easily replace the batteries yourself.
Understanding Your 1999 Mercedes Key Fob System
The “smart key” system in your 1999 Mercedes W210 model is more complex than it might seem at first glance. It actually incorporates three distinct systems:
- Radio Frequency (RF) System: This is what you use for remote operations like locking, unlocking, opening the trunk, and activating the panic alarm from a distance. These functions are powered by the batteries inside your key fob.
- Infrared (IR) System: Working at a closer range, the IR system handles “convenience” features. For example, holding down the unlock button to lower all windows simultaneously. Like the RF system, this also relies on the key fob batteries.
- Drive Authorization System (DAS): This is the security backbone of your Mercedes. The DAS uses an RFID chip within the key, which is inductively powered by the ignition switch when you insert the key. This chip is responsible for authorizing the steering unlock and allowing your car to start. Importantly, the DAS system and the steering lock are independent of the batteries in your key fob.
Many owners mistakenly believe a dead key fob battery will prevent the car from starting or unlocking the steering. However, if your key is still functioning to start the car when inserted into the ignition, but the remote functions (lock/unlock) are failing, battery replacement is likely the solution.
Identifying When to Replace Your Key Fob Batteries
Several signs indicate it’s time for a 1999 Mercedes Key Fob Battery Replacement:
- Reduced Range: You need to be closer to your car than usual for the remote lock/unlock buttons to work.
- Intermittent Operation: The key fob works sometimes, but not consistently, requiring multiple button presses.
- No Response: Pressing the lock or unlock buttons yields no response from your Mercedes, even when close to the vehicle.
If you experience these issues, replacing the batteries is the first and easiest step to take.
Step-by-Step 1999 Mercedes Key Fob Battery Replacement
For your 1999 Mercedes key fob, you will typically need two CR2025 lithium batteries. Here’s how to replace them:
- Locate the Battery Compartment: On the back of your key fob, you will find a small latch or release. This mechanism varies slightly depending on the exact key fob style but usually involves a small button or slider.
- Open the Fob: Carefully use your fingernail or a small, flat tool (like a small screwdriver or butter knife) to release the latch and open the key fob casing. Be gentle to avoid damaging the plastic.
- Identify the Old Batteries: Once open, you will see the two CR2025 batteries. Note their orientation (+ and – sides).
- Remove the Old Batteries: You can usually pry the old batteries out with your fingernail or the same small tool you used to open the fob.
- Insert New Batteries: Install the new CR2025 batteries, ensuring they are placed in the correct orientation (matching the + and – markings in the battery compartment).
- Close the Fob: Carefully reassemble the key fob casing, ensuring it clicks or snaps securely back together.
- Test the Key Fob: Try locking and unlocking your car remotely to confirm the new batteries are working.
Important Considerations After Battery Replacement
- Synchronization: In most cases, your 1999 Mercedes key fob should work immediately after battery replacement without needing to be resynchronized. However, if it doesn’t, consult your owner’s manual for key fob synchronization procedures or seek professional assistance.
- Battery Type: Always use CR2025 lithium batteries for replacement to ensure proper function and longevity.
- Steering Lock and DAS: Remember that key fob batteries do not affect the DAS or the electronic steering lock. If you are experiencing issues with starting the car or steering lock malfunction, battery replacement will not resolve these problems, and further diagnosis may be required. These systems are powered by the RFID chip and the car’s ignition system itself.
- Multiple Keys: Avoid keeping multiple RFID keys for different vehicles on the same keyring. While generally not an issue with modern Mercedes keys, the owner’s manual advises against it.
Replacing the batteries in your 1999 Mercedes key fob is a simple maintenance task that can restore the convenience of your remote functions. By understanding the different systems within your key fob, you can accurately diagnose battery-related issues and address them quickly and efficiently.
