DC/DC converter

The DC/DC converter is located in the luggage compartment in front of the rear power distribution box.

Due to the considerably more frequent occurrence of starting operations, the electrical load that occurs often leads to voltage dips in the vehicle electrical system. To stabilise the supply voltage for certain voltage-sensitive electrical components and protect them, a DC/DC converter is used together with the automatic engine start-stop.

Functional description

The DC/DC converter supplies the terminal 30B DC/DC relay with constant voltage, also during the starting operation. The relay is located in the DC/DC converter.

Index Explanation Index Explanation
1 DC/DC converter bracket 2 DC/DC converter
3 10-pin plug connection

Voltage-critical electrical components are supplied with an equalised voltage if required. This power supply only takes place under certain conditions (starting operation and voltage below 10.5 Volts). Otherwise the connected components are supplied with normal vehicle voltage by bypassing the DC/DC converter.

The DC/DC converter is monitored for diagnosis. The diagnostic cable is read in and evaluated by the junction box electronics (JBE) or the front electronic module (FEM).

Structure and inner electrical connection

The DC/DC converter needs the following signals:

  • Terminal 15N
  • Terminal 30B
  • Terminal 50 (starting operation)
Index Explanation Index Explanation
1 DC/DC converter 2 Electronic component

Pin assignments

Pin Explanation
Terminal 30B Terminal 30, power supply for base operation
Terminal 30B Terminal 30B, power supply for base operation
Terminal 31L Terminal 31, load earth
Terminal 15N Terminal 15, power supply for after-run
Terminal 50 Terminal 50, starting operation
SIG Diagnosis lead

Nominal values

Observe the following nominal values for the DC/DC converter:
Size Value
Voltage range 9 to 16 V
Maximum power consumption 30.5 ± 1.5 A
Temperature range -40 to 85 deg C

Diagnosis instructions

Failure of the component

If the DC/DC converter fails, the following behaviour is to be expected:
  • Fault code entry in the junction box electronics (JBE) or in the front electronic module (FEM)

General notes

The DC/DC converter has diagnostic capability. The following monitoring is available.

  • DC/DC converter OK
  • DC/DC converter faulty
  • DC/DC converter overheated

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