Only trained technicians who have had training in working on a high voltage system should perform this repair. Mercedes DC/DC converter is part of the high voltage (HV) hybrid system and can cause injuries or death when mishandled.
Use a professional bi-direction scanner to power down the high voltage system. With your scanner, go to Battery Management Control Module, then select Deactivate High Voltage System. This option may be under the Acuations menu. Star Diagnostic Scanner is a good scanner that can be used for this step. This step is highly recommended. Working on the high voltage system without powering down the system can cause injuries and even death. This step can not be completed with scanners such as iCarsoft MB II.
Loosen the lug nuts for the front right wheel. Jack up the front right of the vehicle and secure it with jack stands.
Remove the rear splash shield in the front passenger wheel well. Several 10mm nuts need to be removed to be able to take off the splash shield. Locate the DC/DC converter mounted on the frame of the vehicle.
Unplugs the electrical connector that connects to the N83/1 module. You will need to lift the top part of the connector. As you lift the top part, the connecter starts to pull out.
Disconnect the high voltage orange cable connected to the high voltage battery known as HV Battery (A100). Lift the black/blue ring, then pull out the line.
Disconnect the positive cable at the bottom of the DC/DC converter.
Use channel lock pliers to pull down the clamps for the cooling hoses.
Remove the cooling hoses and plug them so that you don't lose all the coolant. Some coolant will be lost, which you will need to add when replacing the DC/DC converter.
Remove the bolt that connects to the ground wire.
Remove all the 8mm nuts that secure the DC/DC converter to the frame.
Remove the DC/DC converter from the vehicle and replace it.
Reconnect the 12-volt battery.
Re-energize the high volt system with a scanner. Clear any fault codes present in the Engine Control Unit, DC/DC control unit, and Battery Management Contol unit.
Check the engine coolant level and add engine coolant. The level will be slightly low due to the coolant you lost in step 8.
The pictures in this guide are from a 2010 Mercedes-Benz S400 hybrid, but the procedure is similar for other Mercedes-Benz hybrid models, including the E-Class hybrid.