How to Open a Mercedes Key Fob: A DIY Repair Guide

Ever accidentally put your Mercedes key fob through the washing machine? It happens! Discovering your car keys soaked after a laundry cycle can be a heart-stopping moment for any Mercedes owner. But don’t panic – it’s often fixable at home. Before you rush to an expensive dealership for a replacement, this guide will walk you through how to open your Mercedes key fob and attempt a DIY repair. With a few simple tools and a bit of patience, you might just save yourself a significant amount of money and get your key fob working again.

Step-by-Step Guide to Disassembling Your Mercedes Key Fob

Opening your Mercedes key fob is the first crucial step in assessing and repairing any water damage, or even just replacing the battery. It might seem daunting, but with the right approach, it’s quite straightforward. Here’s what you’ll need and how to proceed:

Tools You’ll Need:

1. Isopropyl Alcohol (50-70%): Essential for cleaning corrosion and displacing water. You can find this at most pharmacies or supermarkets.
2. Cotton Swabs (Q-tips): For precise cleaning of delicate electronic components.
3. Small Container: To submerge the electronic circuit board in alcohol.
4. Flat Pliers: To gently pry open the key fob casing.
5. Flat Knife or Small Screwdriver: For separating glued components inside the fob.

Opening the Key Fob Casing:

The Mercedes key fob is designed to be secure, but it can be opened without damage if you follow these steps carefully:

1. Extend the Key: Locate the small lever or button that releases the mechanical key blade and extend it fully. This will reveal a small gap in the key fob casing.

2. Insert Pliers into the Gap: Take your flat pliers and gently insert the tips into the gap revealed when the key is extended.

3. Pry Open the Front Half: Carefully apply pressure in the direction indicated by the arrows in the image below. The goal is to gently separate the two halves of the fob casing. Work your way around the seam, gently prying it open. Be patient and avoid using excessive force, which could damage the plastic.

4. Be Mindful of the Spring: As you pry the case open, be aware that there’s a small spring mechanism associated with the key release. Take care not to let this spring pop out and get lost. It’s very small and crucial for the key’s functionality.

Accessing the Internal Components

Once you have successfully opened the Mercedes key fob casing, the next step is to carefully remove the internal components to access the electronic circuit board for cleaning or battery replacement.

1. Remove the Electronic Board: With the casing open, you’ll see the electronic circuit board. Gently push from the battery compartment side to ease the board out of the casing.

2. Handle Battery Terminals with Care: Pay close attention to the battery terminals. These are delicate and can be easily broken if mishandled. Avoid applying force directly to the terminals when removing the board.

Detaching the Transponder and White Plastic Cover

To fully access the circuit board and clean any corrosion, you’ll need to carefully detach the transponder and a white plastic cover that often secures it. These components are typically glued in place and require gentle handling.

1. Apply Isopropyl Alcohol to the White Plastic Cover: Use a cotton swab to apply a few drops of isopropyl alcohol to the edges where the white plastic cover is glued to the transponder. Let the alcohol soak for a minute or two to soften the adhesive.

2. Separate the White Plastic Cover: Carefully insert a small, flat knife or screwdriver between the transponder and the white plastic holder. Gently pry to separate the cover from the transponder.

3. Caution with the Transponder: It’s critical to avoid putting any pressure on the transponder itself during this process. The transponder is a sensitive component, and applying force could damage it, leading to key malfunction.

Removing the Transponder

The transponder is another component that needs to be carefully removed to fully access the circuit board. It is usually glued to the casing and requires a similar approach to the white plastic cover.

1. Apply Isopropyl Alcohol Around the Transponder: Again, use a cotton swab to apply a few drops of isopropyl alcohol around the area where the transponder is glued to the casing. Let it soak for a few minutes to loosen the adhesive.

2. Pry off the Transponder Gently: Insert the small knife underneath the transponder and gently pry it off. Work slowly and patiently to avoid damaging the transponder or the surrounding components.

3. Note the Transponder’s Orientation: Before fully removing the transponder, take a mental note or a picture of its orientation. This will be helpful when reassembling the key fob later.

Cleaning the Electronic Components

With the key fob disassembled and the electronic board accessible, you can now address any water damage or corrosion. This cleaning process is vital, especially if your key fob has been wet.

1. Inspect for Oxidation: Examine the electronic board, particularly the contacts and battery terminals, for signs of oxidation or corrosion. Water damage often leads to a white or greenish buildup on metal parts.

2. Submerge the Board in Isopropyl Alcohol: Pour a generous amount of isopropyl alcohol into your small container. Submerge the electronic circuit board completely in the alcohol.

3. Soak and Agitate: Let the board soak in the alcohol for about 5-10 minutes. The alcohol will help to dissolve oxidation and displace any water trapped on the board. Gently agitate the container occasionally to ensure the alcohol reaches all areas.

4. Clean with Cotton Swabs: After soaking, remove the board from the alcohol and use cotton swabs dipped in isopropyl alcohol to gently scrub away any remaining oxidation, dirt, or debris. Focus on the contacts and any areas with visible corrosion.

5. Allow to Dry Completely: Once cleaned, let all the components, especially the electronic board, air dry completely. This may take about 30 minutes or more. Ensure there is no moisture left before reassembling the key fob.

Reassembling Your Mercedes Key Fob

After cleaning and drying all the components, you are ready to reassemble your Mercedes key fob. This process is essentially the reverse of disassembly.

1. Clean All Parts: Before reassembly, take a moment to clean the plastic casing parts with isopropyl alcohol and cotton swabs to remove any rust, dirt, or residue.

2. Reassemble in Reverse Order: Carefully put all the components back together in the reverse order of disassembly. Ensure the transponder is placed back in its original orientation.

3. Snap the Casing Back Together: Once all internal components are correctly positioned, carefully snap the two halves of the key fob casing back together. Ensure they are securely closed.

Final Check and Battery Replacement

After reassembling your Mercedes key fob, test it to see if it’s working correctly. If you are still having issues, or if you simply want to ensure optimal performance, consider replacing the battery.

1. Test Key Fob Functionality: Try using all the buttons on your key fob to see if they now function correctly. Check if the remote locking/unlocking and other features are working.

2. Consider Battery Replacement: If the key fob is still not working, or if its performance is weak, replacing the battery is a logical next step. Mercedes key fobs typically use CR2025 or CR2032 batteries. Refer to your owner’s manual or check the markings inside the battery compartment for the correct type.

By following these steps, you can effectively open your Mercedes key fob, clean it, and potentially repair it after water damage. This DIY approach can save you time and money compared to dealership repairs. Remember to always handle electronic components with care and patience. Good luck!