This guide will walk you through replacing the auxiliary battery in a 2015 Mercedes-Benz C300 (W205). The “auxiliary battery malfunction” message can be concerning, but the repair is often straightforward. While this issue was covered under warranty, completing the replacement yourself is a viable option if a dealer visit isn’t feasible. The entire process takes approximately 35 minutes.
Replacing the Auxiliary Battery
The auxiliary battery is located beneath the glove compartment. Accessing it requires a few careful steps:
Step 1: Accessing the Battery Compartment
Begin by removing the cover located under the glove compartment. This cover is secured by a single screw and two clips. Once the screw and clips are released, the cover can be removed.
Step 2: Disconnecting the Wiring
Two cables connected to the cover power the glove compartment bulbs. Carefully disconnect these cables to prevent any damage or electrical issues.
Step 3: Removing the Carpet and Plastic Cover
Carefully pull back the carpet behind the glove compartment. It might require some effort, but the foam backing can be gently twisted without causing damage. Once the carpet is pulled back, you’ll see a plastic cover secured by three nuts. Remove these nuts to detach the plastic cover.
Step 4: Replacing the Voltage Converter
With the plastic cover removed, the voltage converter (which houses the auxiliary battery) will be visible. It’s attached to a metal bracket by a clip and a screw. Carefully remove the screw securing the voltage converter. Then, gently detach the clip. Unplug the converter and replace it with the new one.
Step 5: Reassembly
Reassemble everything by following the previous steps in reverse order. Ensure all connections are secure and the carpet is properly placed.
Important Considerations
Exercise caution while working in this area, as there are numerous DC cables beneath the carpet. Accidental damage could lead to electrical problems. Using the correct tools and taking your time will help prevent issues.
This DIY replacement can save you time and potentially money. However, if you are uncomfortable performing this procedure, consult a qualified mechanic. Always disconnect the battery’s negative terminal before starting any electrical work on your vehicle.
