Auxiliary Battery Malfunction In A Mercedes Benz
In this guide, I discuss the auxiliary battery and talk about its location. I will also show you the differences between the main and auxiliary batteries, both of which are important, but for different reasons. Toward the end of this guide, I cover the top symptoms, causes, and fixes of this electrical system fault.
What Does The Auxiliary Battery Malfunction Message Mean?
The Auxiliary Battery Malfunction warning message indicates that something is wrong with the secondary battery system on your Mercedes-Benz vehicle. These batteries – sometimes known as a capacitor – are responsible for secondary functions, such as running electrical components.
When the efficiency and voltage drop too low for the auxiliary battery and the car’s electronic monitoring system detects that, it can result in this warning message on your dashboard.
What is the Auxiliary Battery?
Car Auxiliary Battery
Every passenger vehicle comes equipped with a 12-volt battery that is used to start its engine. The same is true with the Mercedes-Benz lineup of vehicles. However, the German automaker has also installed a second battery in vehicles since the early 2000s.
This second battery is known as the auxiliary battery. It’s a smaller version of the battery that starts the vehicle. In some cases, Mercedes refers to it as a capacitor because of its smaller size.
As with the main car battery, this secondary battery gets charged any time that the engine runs. It also has a similar lifespan, ranging from four to six years. Once it can no longer hold a charge, you might see a warning light illuminate on the dashboard or infotainment system.
Where is the Mercedes Auxiliary Battery Located?
Mercedes-Benz puts the auxiliary battery in multiple locations, depending on which model you drive. If you are looking to replace the secondary battery yourself, you need to know where to look.
The common locations where to find the auxiliary battery on a Mercedes include:
>> In front of the windshield in the engine bay
>> Underneath the front passenger seat
>> Inside the dashboard on the driver’s side
>> Within the engine bay
>> In the trunk
>> Behind the driver’s seat
If you aren’t able to find the auxiliary battery in your Mercedes, you can find the location in your service manual. There are also diagrams available online if you need more support.
Main vs. Auxiliary Battery
The main battery in your Mercedes vehicle is used in every passenger vehicle. It’s also known as the starter battery, system battery or G1. It’s needed to start the motor, and it provides the primary source of power to the car’s electrical systems.
In comparison, the auxiliary battery, known as the G1/7, is the secondary battery. It can also be called the aux battery or backup battery. This battery is usually an AGM battery but could also be a capacitor, depending on how big it is.
Symptoms of Bad Auxiliary Battery Malfunction
If your auxiliary battery is bad, you might see the auxiliary battery malfunction warning light appear on the dashboard. This could be the first warning that the battery isn’t charging as it should. Still, the car will continue running and driving as normal.
With this warning message, your code scanner might be able to pick up the “9062 Component G1/7 (auxiliary battery) is defective or not installed” DTC. Aside from this, you might start to notice trouble with the electrical system features. Depending on what the secondary battery runs, the trouble could be with the infotainment system, radio, and more.
It’s simple to tell when the main car battery dies. When this happens, the motor no longer starts. On the other hand, when the auxiliary battery dies, the symptoms may not be as recognizable.
What Causes An Auxiliary Battery Malfunction Message?
The most common cause of an auxiliary battery error message is a bad auxiliary battery, a bad auxiliary battery relay, or a blown PolySwitch fuse.
Here is some more detailed information about the causes of an auxiliary battery error message:
1. Defective Auxiliary Battery
I’ve already discussed the main reason for the Auxiliary Battery Malfunction message. In most normal cases, the trouble will be the battery itself. This message might give you enough warning to know when the battery is dying before it’s completely dead.
2. Malfunctioning Auxiliary Battery Relay
The battery relay has the important job of deciding when the auxiliary battery needs to be charged. If the voltage drops, the relay sends out the message, ensuring it gets recharged. For this function to work, the engine must be running. Once the relay fails, a warning light can illuminate, and the battery will cease charging.
3. Bad PolySwitch Fuse
The PolySwitch fuse works like a normal fuse, in that it protects from surges and overcurrents. It keeps the flow of electricity within normal ranges.
The difference between the PolySwitch fuse and a typical automotive fuse is that this device will reset itself once a fault gets cleared. Still, if there’s trouble with the PolySwitch fuse, the Auxiliary Battery Malfunction light can come on.
4. Bad Battery Control Module
This module is responsible for measuring the voltage. It handles the monitoring of both the primary and secondary batteries. If this module fails, you can see the Auxiliary Battery Malfunction warning light. It’s also possible to illuminate the primary battery warning light too.
5. CAN Communication Issue
The controller area network (CAN) bus is a networking device that is used in automotive applications. If there’s a problem with this system, it can cause the Auxiliary Battery Malfunction error message. However, it’s not normally a problem with the CAN bus itself. In most cases, the trouble stems from a bad connector or damaged wiring.
How to Fix a Mercedes with Auxiliary Battery Malfunction?
To fix an auxiliary battery malfunction message on your Mercedes, you should start by scanning the error codes with a diagnostic scanner.
Here is some more detailed information on how to fix a Mercedes with auxiliary battery problems:
1. Scan Trouble Codes
Any time you are working with a dashboard warning light, the first step would be to use your code scanner to see what the system is trying to tell you.
In some cases, you may only get generic codes that make it difficult to determine what’s wrong. Other times, there could be multiple codes that paint a more complete picture of what’s going on.
2. Replace Old Auxiliary Battery
If the trouble codes lead you to believe that the problem is with the auxiliary battery, it’s best to replace it first. You can perform this task yourself with some basic tools. The hardest part might be finding the location of the auxiliary battery.
3. Diagnose Electrical System
If changing the auxiliary battery doesn’t resolve the issue, there’s something larger going on. You need to inspect the battery’s relay and the fuse. I’ve covered a few of the parts you need to troubleshoot to get to the bottom of what’s happening.
Use your Mercedes service manual or a repair manual to walk through the appropriate steps. Once you find the faulty part or connection, you can repair it.
4. Seek Help from a Professional
In some cases, the diagnosis might be over your head. When it comes to working with Mercedes vehicles, you want to visit a specialty shop. In many ways, these luxury automobiles are different from the competition, and it’s best to trust a professional.
Can I drive with an auxiliary battery malfunction?
Yes. You can drive with a bad auxiliary battery, but it is not recommended to do so. Your car will still run from the main battery, but you may notice some electrical problems due to the bad auxiliary battery, depending on the car model.
What happens if the auxiliary battery dies?
If your auxiliary battery dies in your Mercedes, in most cases, you will only notice an auxiliary battery malfunction message on your dashboard. You may also notice the 9062 DTC code if you scan the vehicle with an OBD scanner. In rare cases, you may also notice other electronic problems in your car.
Does the alternator charge the auxiliary battery?
Yes. The alternator charges both the main and auxiliary batteries when the engine is running.
Do you have to use a Mercedes auxiliary battery?
No. You don’t need to buy a Mercedes auxiliary battery if you know what you’re doing. But when choosing a battery, it is very important that you choose a battery with the right specifications. Therefore, if you are not sure, it is better to choose a Mercedes auxiliary battery for your specific car model.
After reading this blog post, you should now be aware of the auxiliary battery and why you should not ignore the problem. You should always make sure to check both your batteries regularly and replace them when necessary to avoid issues.