Mercedes-Benz Force Charge 0% Hybrid Battery

A Mercedes-Benz hybrid vehicle, such as an S-Class, E-Class, GLE-Class, etc., may not start if the high-voltage battery is discharged. Typically, the charge level of the hybrid battery needs to be above 28% to start the engine.

Mercedes hybrid vehicles do not have a starter. The electric motor starts the engine, powered by a high-voltage battery, not a 12-volt battery.

Although your dashboard lights are on and your trunk battery is fully charged, the hybrid battery can still be discharged, preventing the engine from starting.

You can charge the high voltage (HV) battery using a 12-volt 50 A charger. An 80A or 100A 12-volt battery charger would charge the HV battery faster. The high-voltage battery can be charged through the 12-volt system through the DC/DC converter.

Requirements

• There are no fault codes related to the hybrid system other than the low battery state of the HV battery.
• An external engine starter charger or connection to another vehicle using jumper cables—12 Volt and 50 Amps or higher output.
• Even though the battery shows 0% on the center console, when checked by the scan tool, it needs to be between 5% and 20% charged. If the battery’s actual charge level has reached o%, it is impossible to charge it using any scanner.

How to charge a hybrid battery

1. Pull the hood release and open the hood.
2. Locate the jump-start terminals for the low-voltage system (12 volts). For example, you must remove the cap on the Mercedes-Benz S-Class to access the positive post.
   – Another option is to connect the external power source, such as jumper cables from a running car, directly to the main 12-volt battery (the manufacturer may not recommend this method, but we have been able to use it successfully).
3. Connect the red clamp of your 12-volt charger to the positive post. 
4. Connect the black clamp from your charger to the ground post near the strut tower. 
5. Get inside the car and turn on the ignition; all dash lights will turn on.
6. Connect a Mercedes-Benz diagnostic scanner to the OBD-II port.
7. Go to control units and select Battery Management System (BMS)
8. You should see the Actuation sub-menu once you connect to this control unit. If you don’t, your scanner may be too basic and need a more advanced scanner.
9. Under the BMS control unit, you can turn on high-voltage battery charging. While the battery is charging, you should see Boost Mode activate. Allow the high-voltage battery to charge. It can take a few hours to charge the hybrid battery. 
10. It can take several hours for the hybrid battery to charge. 

Go to COMAND > System > Hybrid system to verify that the hybrid battery is charging. It shows the small battery symbol with an up arrow. If the up arrow is not showing, the hybrid battery is not charging. The hybrid battery may not charge if active codes exist for the high-voltage system.

Do not leave the vehicle unattended. Monitor the charger to make sure it does not overheat. Depending on the model, the hybrid battery must charge at least 15% to 28% to start the engine.

If the hybrid battery shows 0%, the vehicle will no longer charge that battery. Once the hybrid battery is charged, ideally to at least 30% of its capacity, connect a Mercedes Diagnostic Scanner (SDS) and clear the fault codes in the Battery Management Control Unit. Remember that if the safety contactor in the battery doesn’t close, you will have to close it manually with Star Diagnostic Scanner.

Hybrid Battery Charge Modes

The hybrid system on Mercedes-Benz vehicles operates in one of the following modes.

• Boost mode – The high-voltage battery is charged using the main 12-volt or external 12-volt power. Energy is converted from 12 volts to 120 volts via the DC/DC converter.
• Buck mode: In this mode, power is transferred from the high-voltage battery to charge the main 12-volt battery.
• Passive – There is no power transfer between the high-voltage battery and the 12-volt electrical system.

Warning

• There is a risk of death or injury when working on a high-voltage system. Only trained technicians should work on such systems.
• The vehicle should not be left unattended during the charging process.
• The true battery voltage of the hybrid battery and the charge level shown on the instrument cluster are not the same values.

Get Help

If you are having issues with the hybrid, please “contact the YOUCANIC” team with any questions that you may have.

We can help you troubleshoot the problem FREE of charge as long as you send us the codes.  We need the codes from these four modules:

• Engine ECU,
• DC/DC converter,
• BMS,
• Power Electronics Module.

Once we have the codes, we can tell you if you have a bad power electronic module, hybrid battery, or both.

If your vehicle is at the dealership or mechanic, ask them for a list of CURRENT codes and descriptions and send them to the YOUCANIC team.  Screenshots from Xentry or Snap-on scanner showing current codes work best.

We hope you find the Mercedes-Benz Force Charge 0% Hybrid Battery guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.

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