If you own a Mercedes-Benz, you might have seen a warning message that states, “Auxiliary Battery Malfunction” on the dashboard. What does this warning really signifies, and how can you troubleshoot this issue? It is imperative to know how to solve the Auxiliary Battery Malfunction issue in Mercedes models if you wish to have uninterrupted driving experience.
In this guide, I explain the auxiliary battery, its locations, and how it works. I will explain the main and auxiliary batteries as well, which both hold relevance although for different reasons. Lastly, I go through the leading symptoms, causes, and remedies of this electrical system malfunction.
What Does The Auxiliary Battery Malfunction Message Mean?
The warning message Auxiliary Battery Malfunction indicates a problem with the secondary battery system of your Mercedes-Benz vehicle. These batteries, which on occasion are called a capacitor, are utilized for secondary tasks like running electric parts.
This warning can arise when there is a reduction in efficiency and voltage levels of the auxiliary battery as well as the car’s electronic monitoring system due to detection of the limit.
What is the Auxiliary Battery?
Starting any passenger vehicle needs an auxiliary 12-volt battery and the same is true for the Mercedes-Benz lineup of vehicles. The German automaker has also put in a second battery into vehicles since early 2000’s.
This second battery is known as the auxiliary battery. It is a smaller copy of the vehicle’s starting battery. In some cases, Mercedes refers to it as a capacitor because of the smaller size.
Depending on which Mercedes model it’s installed in, this secondary battery, also known as an auxiliary battery serves a different purpose. It functions as a backup to the main car battery.
In some cases, the battery or capacitor can also be used to power up the engine stop-start system or the stricken keys or the infotainment system.
Like the main car battery, this secondary battery is charged whenever the engine is running. It has an expected lifespan of four to six years. In case of a dead charge, this battery will give out a warning light through the dashboard or infotainment system.
Where is the Mercedes Auxiliary Battery Located?
Depending on the model of your car, you will find the auxiliary battery in different locations. It is important to note the locations if you plan to change the secondary battery yourself.
The locations of the auxiliary battery are listed below:
- 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.
- Directly behind the driver’s seat.
If you are still struggling to locate the auxiliary battery, the service manual for Mercedes has the precise information. Many more documents are available if you are looking for additional guides.
Main vs. Auxiliary Battery
Every passenger vehicle, including Mercedes, features a main battery – the starter battery (system battery, G1). The battery in question is primary to the vehicle’s electrical systems. It is essential to start the motor and for powering the aforementioned systems.
Auxiliary batteries and add-on batteries have the same meaning as the G1/7. Auxiliary batteries or backup batteries are usually AGM batteries, although they can also function as capacitors if they’re large enough. In Mercedes, these batteries are not utilized for starting the engine; however, they do serve to aid the vehicle’s components powered by electricity.
Symptoms of Bad Auxiliary Battery Malfunction
In case of an auxiliary battery malfunction, it is likely that you will notice the auxiliary battery malfunction warning light turned on at the dashboard. This is probably the first hint that the battery is not charging normally. Nevertheless, the vehicle will continue functioning and operating normally.
This warning message might also be captured in the form of a DTC “9062 Component G1/7 (auxiliary battery) is defective or not installed” using a code scanner. In addition to this, you may start observing issues with some electrical system functionalities. Depending on what secondary battery powers, the issues could be in the infotainment system, radio, etc.
When the primary car battery dies, it is easy to tell. The motor ceases to start. With regards to the secondary, when the auxiliary battery dies, symptoms may not be as easily identified.
What Causes An Auxiliary Battery Malfunction Message?
A bad auxiliary battery, a malfunctioning auxiliary battery relay, or even a blown PolySwitch fuse can all trigger an auxiliary battery error message. Additionally, the culprit may also be a bad battery control module, or a wiring issue.
Here is more information concerning the causes of an auxiliary battery error message:
1. Defective Auxiliary Battery
Auxiliary Battery Malfunction message will always have a reason, the main one being the battery. Default scenarios will involve some issue with the battery.
In most scenarios, this battery will have to be replaced, as it ages just like your car battery would. If the message does alert you, then you will have some idea of when the battery is dying.
2. Malfunctioning Auxiliary Battery Relay
One of the essential tasks that the battery relay performs is to decide when the auxiliary battery needs charging with respect to relays. If the voltage drops, the relay does notify ensuring replenishment.
The engine has to be running for this function to operate. When the relay malfunctions, the system warning light might be illuminated hence the cessation of charge to the battery.
3. Bad PolySwitch Fuse
The Poly Switch fuse also works just like an ordinary fuse, in that it protects from surges or overcurrent. Poly switch fuses function just like any ordinary fuse as they prevent overload current or voltage.
The Poly Switch fuse differs from a standard automotive fuse in that this device resets automatically once a malfunction is cleared. However, if there is an issue with the PolySwitch fuse, the Auxiliary Battery Malfunction light may illuminate.
4. Bad Battery Control Module
This module monitors the voltage. It controls the supervision of the primary and secondary batteries.
If this module fails, the Auxiliary Battery Malfunction warning light may come on. Furthermore, the Primary Battery warning light may also turn on.
5. CAN Communication Issue
CAN bus refers to a communication network system used in vehicles. If there is a fault within this system, it will trigger the Auxiliary Battery Malfunction error message.
Usually, the CAN Bus is not the issue. Most of the time, the problem is a faulty connector or broken cable.
How to Fix a Mercedes with Auxiliary Battery Malfunction?
To resolve the auxiliary battery malfunction message in your Mercedes, it is prudent to begin by diagnosing the vehicle with a diagnostic scanner. After that, check the suspected faulty relay and fuse of the auxiliary battery, and replace them as necessary.
Here is how to fix a Mercedes with auxiliary battery problems more precisely:
1. Scan Trouble Codes
When working with any dashboard warning light, the initial approach is to plug in your code scanner and see what the system is trying to communicate. If there are too many codes set, it may be a good idea to clear them and perform a drive cycle, checking the codes again afterwards.
Sometimes, you may discover that you only have access to generic codes, which is often less useful. It is also possible that there are many codes which are more useful when looked at as a combined set.
2. Replace Old Auxiliary Battery
If the diagnosis points to an auxiliary battery issue, I suggest replacing the battery first as most of the time this warning light is triggered because the battery has been used till it is completely drained and it stops charging.
Because of this, any battery older than four years should be deemed to be replaced. This is a bolt-on job that can be performed by anyone with basic hand tools. Locating the auxiliary battery may be the hardest part of the process.
3. Diagnose Electrical System
Consider other options if changing the auxiliary battery doesn’t fix the problem. It would be best if you checked the relay of the battery and the corresponding fuse. I have gone over some of the components that you need to troubleshoot in order to understand what is going on.
Follow the procedures as documented in the Mercedes service manual or your preferred repair manual. After locating the broken part or connection, make the necessary repairs.
4. Seek Help from a Professional
You may find other aspects of the diagnosis somewhat difficult. If you lack the appropriate code scanner, or lack the knowledge to work on a Mercedes, consider taking the car to a local repair shop.
Consider a specialized shop that deals with Mercedes cars. Unlike cars from other companies, these luxury automobiles are quite unique, so it is advisable to leave it to a professional.
Can I drive with an auxiliary battery malfunction?
Yes. Certainly, driving with a faulty auxiliary battery is possible, though it is ill-advised. In any case, the vehicle will operate using the primary battery, and depending on the make and model of the vehicle, some electrical issues might be experienced due to the faulty auxiliary battery. Hence, you should resolve the issue as soon as you can.
What happens if the auxiliary battery dies?
For most users, all that will happen is that the message indicating that the auxiliary battery is malfunctioning will show up on the dashboard of the car. If you use some form of diagnostic scanner on the vehicle, you may also find that the 9062 DTC code is present. On rare occasions, some other electronic faults may also be observed in the vehicle.
Does the alternator charge the auxiliary battery?
Yes. The alternator charges both the main and auxiliary batteries when the engine is running. There is a relay for the auxiliary battery that opens and closes the circuit when the auxiliary battery should be charged by the generator.
Do you have to use a Mercedes auxiliary battery?
You do not have to purchase a Mercedes auxiliary battery if you understand what you’re doing. It’s critical to remember that you must check the specifications of the battery you plan to use. It is almost always better to select a Mercedes auxiliary battery for your car make and model if you are uncertain.
In most cases, the auxiliary battery malfunction alert is generated due to a faulty auxiliary battery or its relay or fuse. If you know that the auxiliary battery has been replaced a long while back, it would make sense to change it now even if you suspect it is not the case at the moment.
I trust this blog has made you knowledgeable about the dangers of ignoring the auxiliary battery and the issues surrounding it. You ought to bear in mind that the two batteries have to be checked and maintained consistently to mitigate the challenges that may arise.