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Mercedes-Benz E 350 Auxiliary Battery Malfunction - How To Troubleshoot And Fix

Your Mercedes-Benz E 350 has two batteries - a regular 12-volt starting battery and a smaller, secondary auxiliary battery used to keep all electrical components turned on. These electrical components include GPS, instrument cluster, navigation, and radio, as well as safety features such as Blind Spot Assist and Active Brake Assist. The auxiliary battery is not intended for starting or running the engine.

If your system voltage becomes low, you can use the auxiliary battery to manage some of the more critical vehicle components.

On occasion, your Mercedes-Benz E 350’s auxiliary battery may go bad due to regular wear and tear or sudden impact. On average, auxiliary batteries last up to seven years before needing repair or replacement.

Keep reading to learn more about your Mercedes-Benz E 350's auxiliary battery, including the E 350 auxiliary battery location, instructions on how to replace auxiliary battery Mercedes-Benz E 350, and how to fix/replace the auxiliary battery.


Where is Your Mercedes-Benz E 350’s Auxiliary Battery Located? 

Your Mercedes-Benz E 350’s auxiliary battery is under the hood, near the cabin air filter housing. It should take no more than 20 seconds to locate.


How Do I Know I Have a Faulty Auxiliary Battery? 

There are many indicators of a Mercedes-Benz E 350’s faulty auxiliary battery. The first sign is a flashing onboard computer error that either flashes or stays on. It can also appear as a small battery symbol.

An ODB-II diagnostic scanner can also pinpoint specific issues, including a faulty auxiliary battery.


What Are The Causes of Faulty Auxiliary Battery? 

There are a few reasons why your Mercedes-Benz E 350’s auxiliary battery may go bad. One key issue is damage done to a voltage converter, responsible for changing a power source's electrical output. It allows 12-volt power devices in your vehicle to run effectively.

Another sign of a defective Mercedes-Benz E 350 auxiliary battery is fluid leakage. If you don't treat fluid leakage in time, it can corrode and rust your engine, requiring a more costly fix or replacement.


Is It Safe To Drive with a Faulty Auxiliary Battery? 

Generally, we do not recommend driving with a faulty Mercedes-Benz E 350 auxiliary battery.


Replacement Instructions for Your Mercedes-Benz E 350's Auxiliary Battery

Here are the steps needed to replace an old Mercedes-Benz E 350 auxiliary battery with a new auxiliary battery. For this task, you will need a 10mm wrench.

  1. Remove the housing that covers the auxiliary battery.
  2. Use a 10mm wrench to loosen the ground line bolt and remove it from the battery.
  3. Remove the positive ground line from the battery.
  4. Loosen the battery's hold down bracket nut and fold the hold-down bracket back.
  5. Remove the old auxiliary battery.
  6. Install the new auxiliary battery, completing all of the above steps in reverse order.
  7. Reinstall the positive line onto the positive battery terminal and reinstall the negative line to the negative battery terminal before reinstalling the housing.
  8. Perform a quick 5-minute test drive to ensure all of your electrical components are working. Pay attention to LED lighting, entertainment center radio, and safety features such as Lane Assist, Blind Spot Assist, and Active Brake Assist.

Do not forget to remove your Mercedes-Benz E 350's primary car battery's connectors before removing the auxiliary battery. This is very important. Failure to do this may result in shortages or sparks.

All in all, one can easily replace the whole Mercedes-Benz E 350 auxiliary battery, even with moderate mechanical skills. Be sure to seek all replacement parts from the Mercedes-Benz national store. If you are looking for a replacement auxiliary battery, please consult with your Mercedes-Benz E 350's owner's manual for the exact one needed.