Is the auxiliary battery in Mercedes Benz covered under warranty?

This blog will provide answers to the following questions: Is the auxiliary battery in Mercedes Benz covered under warranty? What is an auxiliary battery malfunction? What are the functions of an auxiliary battery in Mercedes Benz cars? 

Is the auxiliary battery in Mercedes Benz covered under warranty?

Yes, the auxiliary battery in Mercedes Benz is covered under the standard warranty. In case of any auxiliary battery malfunction, customers can report to dealerships and claim the new battery with associated labour costs with it.

Following are the two types in which the auxiliary battery can be replaced under warranty.

Standard warranty

Mercedes Benz’s standard warranty covers bumper-to-bumper components. In case there is an Auxiliary battery malfunction in the vehicle, customers can report to authorised workshops for further diagnosis.

The further diagnosis steps for the auxiliary battery malfunction problem include checking the condition of the battery. A Mercedes Benz diagnosis tool is used to record the actual values of the auxiliary battery.

A visual inspection is carried out of the fuse and battery terminals. After all the checks are completed; a technical product report is generated and the warranty claim can be raised. The auxiliary battery is replaced free of cost and the old battery is returned to the warranty department in the authorised dealership.

The warranty claim can be rejected if there is accidental damage or unauthorised fitment on the battery. Mercedes Benz battery monitoring systems are all interlinked and installing a component directly on the battery can cause the battery to drain.

Parts warranty

When the customer pays for a new auxiliary battery, Mercedes Benz gives a 2 years parts warranty. In such cases, if the customer gets an auxiliary battery malfunction problem before the end of 2 years; then the auxiliary battery can be replaced under warranty.

There is no warranty for an auxiliary warranty that has already been replaced under a part warranty or standard warranty. Therefore, it is necessary to identify the correct cause of the auxiliary battery malfunction.

The park pawl capacitor found in the new cars is also eligible for a parts warranty. The main battery is used for charging the auxiliary battery. Hence, the condition of the main battery must be good.

If the auxiliary battery is replaced without checking the condition of the main battery then it can lead to repeat repairs. The front sam control unit performs a quick actuation of the auxiliary battery relay when the vehicle speed exceeds 20 km per hour for the first time since the engine started.

The auxiliary battery is connected to the onboard electrical circuit momentarily and once the actuation of the relay is okay, the front sam control unit can then continue to monitor the state of charge for the main battery and the auxiliary battery.

In the Eco start-stop mode, the front SAM can allow up to 7-9 engine starts before the auxiliary battery voltage goes down. In that situation, the green LED on the ECO start-stop switch will not light up and the instrument cluster will also show the ECO sign in yellow colour. 

What is an auxiliary battery malfunction?

An auxiliary battery malfunction means that the power supply in the auxiliary battery is not within the specified limit of 11.5 to 14.5 volts. The front signal acquisition and actuations control unit monitors the voltage of the auxiliary battery and generates a fault code when the voltage goes out of range.

When the fault code is stored in the DTC memory of the front signal acquisition and actuations control unit; a message ‘ auxiliary battery malfunction’ is displayed in the instrument cluster. The message is in yellow colour which means it is not a critical fault that can cause a breakdown.

The remedy for the auxiliary battery malfunction is to check the battery voltage and restore the auxiliary power supply by replacing the auxiliary battery. In some cases, the electrical fuse on the signal can also blow due to an internal fault in the battery.

In the latest Mercedes Benz cars, a park pawl capacitor is installed in the place of an auxiliary battery. Mercedes Benz introduced this technical modification in order to reduce the cost of repair as a small capacitor is sufficient to perform the function of engaging the emergency parking brake.

What are the functions of auxiliary batteries in Mercedes Benz cars?

The auxiliary battery in Mercedes Benz cars has the following functions :

Power supply during eco start-stop mode:

The engine cut-off or ECO is an automatic start-stop system which is used to increase the fuel economy by turning off the engine at stop signs or traffic signals. When the system is ready, a green ECO symbol appears in the instrument cluster.

The indication LED on the eco switch in the lower panel also turns green when the system is ready for automatic engines to stop and start. As the engine is started in the ECO function, the starter motors can bring the main battery voltage down to 9–10 Volts.

This voltage is not sufficient to keep the onboard electrical systems and creature comfort running. Therefore, an auxiliary battery is connected to the main power supply of the vehicle via a dedicated relay.

The battery voltage of the auxiliary battery is 12V and as it only supports the vehicle power supply when the main battery is used to crank the engine, the battery capacity and the size can be small.

Most of the auxiliary batteries in the models with engine cut-off function are 12 volts 170-200 Amps. The location can be in the passenger footwell for the new generation cars like A, B, GLA, CLA etc. in the sedans it is located in the luggage compartment and the auxiliary battery relay is also next to the battery.

Emergency parking brake actuation

This function is activated only when the main battery is either disconnected or completely discharged. The electronic ignition lock gets an auxiliary power supply for the auxiliary battery and if the main battery voltage goes to 0 V; the parking gear is engaged.

In the latest models, a capacitor is used to engage the parking gear if the vehicle is not in P. Once the capacitor discharges, it is not possible to release the parking gear until the main battery voltage is restored.

If there is an electronic parking brake then the auxiliary battery can also engage the parking brake along with the P gear to protect the vehicle against theft/ unauthorised towing.

Conclusion

This blog explained the ways under which the auxiliary battery in the Mercedes Benz car is covered under warranty. The auxiliary battery is responsible for critical functions in case the main battery is discharged. The auxiliary battery is connected to the main battery and continuing to use the vehicle with an auxiliary battery malfunction will eventually damage the main battery.

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