Auxiliary Battery Malfunction

Auxiliary battery malfunction: meaning, causes, and how to fix

The auxiliary battery is essential to the running of your Mercedes-Benz C 300. Without it, your instrument cluster, dashboard warnings, and other electronic parts like GPS won’t turn on, which will affect how you drive overall. Read on to find out more about auxiliary batteries, C 300 auxiliary battery malfunctions, their causes, and how to fix them. A message displaying “Auxiliary Battery Malfunction” may have shown on your dashboard if you drive a Mercedes-Benz. If you want to have a reliable drive, you should be able to fix Mercedes models’ Auxiliary Battery Malfunction.

Auxiliary Battery Malfunction

Well, in this article, we’ll be discussing the answers to the following questions:

  • What is an auxiliary battery?
  • What does the auxiliary battery malfunction mean?
  • How does an auxiliary battery work?
  • What causes the auxiliary battery malfunction warning to come on?
  • Can you drive with the auxiliary battery malfunction message on?
  • How to fix the auxiliary battery malfunction?
  • What’s the cost to replace an auxiliary battery?

Read more: Battery light on in car: meaning, causes, what to do when the light appears on the dashboard

Ok, let’s dive in!


What is an auxiliary battery?

An auxiliary battery is a secondary battery in a vehicle that is used to power the vehicle’s electrical system when the main battery is unable to provide enough power. The main battery in many modern cars is primarily made to start the engine and power the car’s accessories while the engine is running. The capacity of the main battery, however, could not be adequate to run all of the car’s electrical equipment when the engine is off. The auxiliary battery takes over in these circumstances and powers the car’s electrical system.

Auxiliary Battery

Auxiliary batteries are frequently found in hybrid, electric, and start-stop vehicles, which turn off the engine while the vehicle is stopped to conserve fuel. They are occasionally used in recreational vehicles (RVs) and other automobiles that need a lot of electrical power to run appliances and other gadgets. Auxiliary batteries work in conjunction with your primary starter battery and as a backup battery in the event that the primary battery fails.

It keeps your radio, GPS, and other in-vehicle electrical components powered on and stops your vehicle’s electrical components from dropping when you start or stop the engine. Any voltage converter issue will often result in an erroneous fault message being shown on your instrument cluster. A little battery icon can emerge, or an onboard computer error fault message might state that the “auxiliary battery malfunction.” Every time you start your car, you will notice it right away until a proper diagnosis (and possible replacement) can be made by you or a qualified mechanic.

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What does the auxiliary battery malfunction mean?

The auxiliary battery malfunction is an error or warning message that indicates there is an issue with the vehicle’s auxiliary battery system. Depending on the precise make and model of the car, the message’s exact meaning may vary, but generally speaking, it indicates that the onboard computer of the car has identified a problem with the auxiliary battery or the system that controls it. A number of problems, including a weak or dead auxiliary battery, an unreliable alternator, a broken voltage regulator, or an issue with the auxiliary battery control module, could be the precise reason for the malfunction.

Auxiliary battery problems can result in a variety of problems, including difficulty starting the engine, dim lights, and broken electrical components. Your car’s electrical systems and operations may have issues because of a faulty auxiliary battery. The radio, GPS, PDC sensors, entertainment system, and start/stop capabilities are a few of these. As time goes on, you may begin to notice that safety features on your car, including Blind Spot Assist and Lane Keeping Assist, don’t work. Your instrument cluster may also turn on the AUX battery light.

Please take note that as these are not essential parts, your car won’t start. Nevertheless, if you depend on any of these useful safety functions, like Lane Assist, they may impair your ability to focus on the road. Whenever an auxiliary battery malfunction message or warning light appears, it’s crucial to get the problem identified and fixed right away. Driving with a damaged auxiliary battery might cause the car’s electrical system to become much more damaged or perhaps completely fail, leaving you stranded on the road.

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How does an auxiliary battery work?

The specific vehicle and its electrical system determine how an auxiliary battery works. In general, though, the auxiliary battery works by supplying electricity to the car’s electrical systems when the primary battery is unable to do so. The electric motor and other electrical systems of a hybrid or electric car are normally powered by the auxiliary battery when the car is in electric-only mode or when the engine is off.

When the engine is running, the main battery of the car and/or regenerative braking both charge the auxiliary battery. The auxiliary battery is used in vehicles with start-stop systems to keep the accessories running even while the engine is off. When the engine is operating, the main battery of the vehicle often charges the auxiliary battery. The auxiliary battery is intended to act as a backup power source for the car’s electrical system in both scenarios, in case the primary battery fails or is unable to supply adequate power.

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What causes the auxiliary battery malfunction warning to come on?

Here are the most common causes of auxiliary battery malfunction coming on:

Faulty Auxiliary Battery

The primary cause of the Auxiliary Battery Malfunction warning message is a faulty auxiliary battery. Typically, the battery itself will be the problem. Like your car’s batteries, the battery needs to be replaced as it gets older. You might be able to tell when the battery is deteriorating from this message before it goes fully dead.

Auxiliary Battery Relay failed

The crucial task of determining when the auxiliary battery needs to be charged rests on the battery relay. The relay transmits the message in the event of a voltage decrease, ensuring that it is recharged. The engine must be operating in order for this feature to function. When the relay malfunctions, the battery won’t continue to charge and a warning light may come on.

Bad Battery Control Module

This module is in charge of measuring voltage. Both the primary and secondary batteries are monitored by it. You can observe the Auxiliary Battery Malfunction warning light if this module fails. Moreover, the primary battery warning light may be turned on.

Defective PolySwitch Fuse

The PolySwitch fuse functions similarly to a standard fuse in that it guards against surges and over-current. It maintains the electrical flow within acceptable limits. The PolySwitch fuse differs from a standard automotive fuse in that it automatically resets after a fault is fixed. However, the Auxiliary Battery Malfunction light may turn on if there is a problem with the PolySwitch fuse.

CAN Communication malfunction

A networking tool used in automotive applications is the controller area network (CAN) bus. This mechanism may malfunction and result in the Auxiliary Battery Malfunction error message. However, the CAN bus itself typically isn’t the issue. The problem is typically caused by a faulty connector or frayed wiring.

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Can you drive with the auxiliary battery malfunction message on?

Can you drive with the auxiliary battery malfunction message on?

The particular circumstances and the seriousness of the problem determine whether it is safe to drive while the auxiliary battery malfunction warning is on. It might be safe to drive the car for a short distance, like to a nearby service station or repair shop, if it is still starting and working correctly and you only occasionally notice the warning message or light. The auxiliary battery might not be able to supply enough power to keep the car’s electrical systems functioning properly, therefore you should avoid using the vehicle for a long time.

You shouldn’t operate the car at all if the auxiliary battery is totally dead or if the warning message is backed by additional symptoms like trouble starting the engine, dimming lights, or broken electrical parts. A damaged electrical system or a full loss of power could result from continuing to drive with a bad auxiliary battery, leaving you stranded on the road. In order to prevent further harm to the vehicle and ensure safe driving, it is often essential to have the problem identified and remedied as soon as possible.

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How to fix the auxiliary battery malfunction?

Here’s how to fix the auxiliary battery malfunction warning:

  • Check the auxiliary battery.
  • Examine the charging system.
  • Check the auxiliary battery control module.
  • Reset the warning message.
  • Consult a professional.

Check the auxiliary battery:

Checking the auxiliary battery to verify if it is dead, weak, or damaged is the first step. It will really be necessary to replace the battery if it is weak or dead. In the event that it is damaged, it will need to be replaced or repaired.

Examine the charging system:

It is important to examine the alternator and voltage regulator in the charging system to make sure they are working properly. The auxiliary battery may not be able to charge adequately and finally fail if the charging device is malfunctioning.

Check the auxiliary battery control module:

The auxiliary battery’s charging and discharging are controlled by the auxiliary battery control module. If the module is broken, it might need to be fixed or replaced.

Reset the warning message:

You might need to reset the alert message or light to make it go away if the problem has been fixed. Normally, you may accomplish this by disconnecting the battery for a short while or resetting the system with a diagnostic tool.

Consult a professional:

The best course of action is to get assistance from a qualified mechanic or approved service shop if you’re unsure how to tackle the problem yourself or if it keeps coming up despite your efforts to fix it.

In general, it’s critical to identify and address any problems with the auxiliary battery as soon as possible in order to limit further harm to the car’s electrical system and ensure safe operation.

What’s the cost to replace an auxiliary battery?

The make and model of the car, the type of battery needed, and the labor costs involved will all have an impact on the price of replacing an auxiliary battery. A new auxiliary battery can often be purchased for $50 to $300, depending on the battery type and the make and model of the car. However, depending on the difficulty of the installation and the mechanic’s or service center’s hourly rate, the cost of labor to replace the battery can also differ greatly.

To replace the auxiliary battery on some contemporary vehicles, you might also need specialized tools or equipment, which will increase the cost. Also, if the charging system or the auxiliary battery control module has additional problems, they might also need to be fixed or replaced, which would raise the entire cost. Depending on the particulars, replacing an auxiliary battery can cost anywhere from $100 to $1,000 or more in total. Before beginning any repairs, it’s always a good idea to receive a comprehensive estimate from a reliable mechanic or service facility.

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What does auxiliary battery malfunction mean on Mercedes?

The auxiliary battery receives power from the operating engine, just as the primary battery. It also has a lifespan of four to six years, just like the main battery. The computer displays an error message when it is unable to hold a charge.

Can I drive with an auxiliary battery malfunction?

Like all other automotive parts, auxiliary batteries deteriorate over time, so you will ultimately need to replace one. Driving is not suggested if your auxiliary battery is giving you trouble.

What happens if the auxiliary battery dies?

The vehicle will usually start after being jumped off, but it will immediately shut off after being turned off. This is because the vehicle’s alternator provides it with the necessary charging when the engine is operating.

Do I need to replace the auxiliary battery?

Auxiliary batteries typically last between 5 and 8 years, though this can vary. Nevertheless, as soon as your auxiliary battery starts to deteriorate, the rest of your vehicle will start to suffer. Accessories may begin to break down, and other auto systems may develop problems.

Can an auxiliary battery stop the car from starting?

An issue with your auxiliary battery might not be as noticeable as one with your starting battery. Your automobile will still start and operate normally. You might find that certain accessories don’t work at all or only partially.

Can you drive a Mercedes without the auxiliary battery?

The simple answer is both yes and no. Get your Mercedes into a licensed repair shop as soon as you can if you need to replace the auxiliary battery. Nonetheless, after the warning lights turn on, it is usually safe to continue driving for up to 100 miles.

Can an auxiliary battery drain the car battery?

If your system isn’t wired properly, the backup battery could drain the main battery. Because of this, it’s crucial to have an isolator or charge controller that only permits electrical current to travel in one direction.

Can an auxiliary battery be recharged?

This indicates that while the starter battery is not in use, the auxiliary battery can serve additional consumers in a reliable manner. The alternator can then be used to replenish both batteries while you’re traveling.

That is all for this article, where the answers to the following questions have been discussed:

  • What is an auxiliary battery?
  • What does the auxiliary battery malfunction mean?
  • How does an auxiliary battery work?
  • What causes the auxiliary battery malfunction warning to come on?
  • Can you drive with the auxiliary battery malfunction message on?
  • How to fix the auxiliary battery malfunction?
  • What’s the cost to replace an auxiliary battery?

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