Mercedes › Resources

By YOUCANIC on Jan 2, 2019

Mercedes-Benz K57/2 Auxiliary Battery Relay Replacement

In this guide, you will find instructions on how to replace the auxiliary battery relay (K57/2) on Mercedes-Benz vehicles. Mercedes auxiliary battery relay is typically mounted at the top of the firewall, right below the windshield wiper motor. 

If you have replaced the auxiliary battery and are still getting "Auxilary battery malfunction" there is a chance that the auxiliary relay may be the culprit. 

Mercedes-Benz K57/2 Auxiliary Battery Relay Replacement

What you will need


  1. Park your Mercedes-Benz and set the parking brakes. Remove the key from the ignition. parked mercedes
  2. Open the hood by pulling the release under the dashboard. 
  3. Next, you need to remove the wiper arms. Remove the 13mm bolt on the wiper arm. Pull up the arm to remove it from the shaft. remove wiper arm
  4. Remove the plastic trim. There are four plastic retainers that need to be removed before you can remove the plastic trim. remove plastic trim
  5. Locate the auxiliary battery relay mounted on the firewall. Remove the two bolts that hold the auxiliary battery in place. Unplug the electrical connector and replace. Mercedes auxiliary battery relay location

This guide only shows how to replace the auxilary battery relay. To learn how to replace the auxiliary battery itself, follow the guide on How to change Mercedes-Benz auxiliary battery.


Plain text

  • Allowed HTML tags: <a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type='1 A I'> <li> <dl> <dt> <dd> <h2 id='jump-*'> <h3 id> <h4 id> <h5 id> <h6 id>
  • No HTML tags allowed.
  • Lines and paragraphs break automatically.
  • Only images hosted on this site may be used in <img> tags.