What Causes Auxiliary Battery Malfunction Mercedes? [Quick Effective Solutions]

“Auxiliary Battery Malfunction” warning message on the dashboard is a common issue Mercedes users encounter. So, if you have a Mercedes or looking to buy one, you should be aware of the message so that you can fix the problem easily.

However, before fixing the issue, you should know: What causes auxiliary battery malfunction Mercedes?

Several reasons can typically cause “Auxiliary Battery Malfunction” in Mercedes. Some common causes include a bad auxiliary battery itself, malfunctioning battery relay, faulty PolySwitch fuse, bad battery control module, and CAN communication issues.

Read the entire content if you want more details about the “Auxiliary Battery Malfunction” message. Here you’ll find a comprehensive discussion of the reasons behind this problem and possible solutions.

What Does Auxiliary Battery Malfunction Message Mean On Mercedes?

An auxiliary battery typically works as a backup battery on Mercedes. It helps to run the car’s electrical components, including light, audio, and air conditioners.

When something happens wrong with the auxiliary battery, a message saying “Auxiliary Battery Malfunction” will appear on the dashboard of the Mercedes.

This problem can occur for different reasons. For example, when the voltage of the auxiliary battery drop too low, the warning message will appear on your Mercedes dashboard.

What Causes Auxiliary Battery Malfunction Mercedes?

As we said, several reasons can lead “Auxiliary Battery Malfunction” warning message on your Mercedes dashboard. Some of the common reasons for having this problem have been explained below.

Bad Auxiliary Battery

A bad auxiliary battery is a common reason for this problem in Mercedes. We all know that the nature of batteries is to degrade over time, and after a certain time, the battery will die completely. So, if your Mercedes has an old auxiliary battery, you may see the “Auxiliary Battery Malfunction” warning message on the dashboard.

Malfunctioning Battery Relay

The battery relay is responsible for charging the battery in time. Typically, when the voltage of the auxiliary battery drops, the relay sends the message, resulting in the battery being recharged. In that case, if the relay malfunction, the auxiliary battery can’t be recharged, which leads to illuminating the warning message.

Faulty PolySwitch Fuse

PolySwitch fuse is similar to typical automobile fuses, which protect electronic components from overcurrents and surges. The only difference between these fuses is that PolySwitch resets itself once the faulty is fixed. So, wherever any fault occurs with PolySwitch, the electric components won’t get electric currents, causing the warning message to come on the dashboard.

Bad Battery Control Module

The battery control module typically measures the voltage and sends the required running voltage to the electric components. Apart from that, this module also monitors the primary battery activities. In that case, if the control module malfunctions, the warning message will come on the dashboard.

CAN Communication Issue

A controller area network (CAN) bus is a networking device that connects all the electrical equipment together. Although the CAN bus doesn’t directly connect to the auxiliary battery, malfunctioning the bus will also cause an error message on the dashboard. This problem mainly occurs when loose connections or faulty wiring are associated with the auxiliary battery.

How to Fix Auxiliary Battery Malfunction On Mercedes?

After knowing the reasons for the “Auxiliary Battery Malfunction” on Mercedes, you may be thinking about how to solve the problem. That’s why here in this section, we’ve discussed solutions for this warning issue.

1. Examine the Auxiliary Battery

First, you’ll need to check the auxiliary battery to see if the battery is weak, damaged, or dead. You can use a code scanner to check the battery life at this stage. If the battery is weak or damaged, you may replace it with a new one. In general, an auxiliary battery should be replaced after four years of use. However, if you find the battery’s health is good, you’ll need to locate other reasons that can cause the problem.

2. Make Sure The Charging System Is Working

Once you’ve found the battery is in good health, you should check the battery’s charging system. An auxiliary battery is usually charged through the alternator, similar to the primary battery. For that, you’ll need to check whether the alternator can charge the auxiliary battery properly in your Mercedes. However, you should also check the voltage regulator or battery relay. If the voltage regulator or battery relay fails, the auxiliary battery won’t charge.

3. Fix The BCM (Battery Control Module)

As we know, the BCM (Battery Control Module) controls the auxiliary battery’s charging. So, if the control module malfunction, the “Auxiliary Battery Malfunction” will appear on your Mercedes’s dashboard. In that case, you must fix or replace the BCM with a new one.

4. Reset The Warning Message

If the problem is not fixed even after following the process above, you have to reset the warning message. Resetting the alert message may help to go away the illuminated warning light. To reset the alert, you must disconnect the auxiliary battery for a while or reset the entire car computer system with the right procedure.

5. Seek the Help of Professionals

It will be best to seek the help of an expert mechanic or an authorized service center if you are unable to fix the problem. They will diagnose your Mercedes auxiliary battery with the right code scanner and suggest what you have to do. In that case, if you need to replace the battery or any other component, they will help you to get these.

Can I Drive Mercedes With Auxiliary Battery Malfunction?

Yes, driving a Mercedes with an auxiliary battery malfunction is possible. However, it is not recommended to do so. Although your primary battery will work properly, you may notice some electrical issues due to a bad auxiliary battery.

This will be a serious problem when driving Mercedes on the highway, when you may find some electric components are not working. So, you should fix or replace the battery as soon as you notice the “Auxiliary Battery Malfunction” alert on your Mercedes.

Some Frequently Asked Questions About Auxiliary Battery

Mercedes’ owners have different questions about the auxiliary battery. For that, here we’ve explained some common questions regarding that. Check the section for any question you are looking for; you may find your desired answer here.

What Is The Life Span Of The Mercedes Auxiliary Battery?

The lifespan of the Mercedes auxiliary battery mainly depends on several factors, especially how well the battery is taken care of. However, you can expect the life span of an auxiliary battery to be around 4 years of the 12-volt battery.

How Much Does Auxiliary Battery Cost for Mercedes?

The average cost of an auxiliary battery cost between $200 to $300. However, you may need to spend $50–$100 more in labor costs when replacing the battery. In that case, you can save spending additional money by replacing the battery yourself.

What Are The Signs Of Having A Bad Auxiliary Battery On Mercedes?

Several signs you’ll notice if your Mercedes have a bad auxiliary battery. First of all, the “Auxiliary Battery Malfunction” warning message will appear on your Mercedes dashboard. You may also notice some trouble with the electrical system features, including radio, air conditioner, and more.

Can A Bad Auxiliary Battery Cause To Drain The Main Battery In Mercedes?

Yes, a bad auxiliary battery can drain the main battery in your Mercedes. Since an auxiliary works as a backup battery, if it doesn’t work properly, the main battery will need to power the electric components, causing the battery to drain.

Do All Cars Have Same Size Auxiliary Batteries?

No, auxiliary batteries’ sizes can vary depending on the car’s brands and models. Apart from size, auxiliary batteries’ design, capacity, amount of required maintenance, and cost can differ from brand to brand. However, all auxiliary batteries have the same 12-volt voltage.

Final Thoughts

Although you can drive your Mercedes with a malfunctioning auxiliary battery, you should repair or replace the battery. However, before fixing the issue, you should know: What causes auxiliary battery malfunction Mercedes?

Hopefully, you may have already understood what causes the “Auxiliary Battery Malfunction” message on your Mercedes. Typically, having a bad auxiliary battery, faulty battery relay, and malfunctioning battery control module are the main reasons for causing this problem.