Airbag control unit with part number A0285013856

What does the airbag control unit A0285013856 do?

The airbag control unit A0285013856 forms the central control of the restraint system (SRS) in Mercedes-Benz. It reads the signals from the crash sensors, decides within milliseconds whether to trigger the airbags and seatbelt pretensioners in an accident, and monitors the system continuously. After an accident it stores crash data and locks itself.

It shows irregularities via the airbag warning light in the instrument cluster. The sensors and the triggering logic work closely together, and the unit links both sides.

Why does the control unit A0285013856 fail?

The most common cause is crash data stored after an accident, even if no airbag was triggered; a normal diagnostic tool cannot erase it. Other possible causes include ageing electronic components, cold solder joints, moisture and corrosion on plug connections, and voltage spikes, for example from a weak battery or jump-starting.

The crash data stay in the memory because of the nature of the memory itself. As a result, the fault persists even when nothing unusual shows up in everyday driving.

The other causes concern the electronics themselves. Components age, solder joints can go cold, and moisture or corrosion damage the plug connections. Voltage spikes, for example from a weak battery or jump-starting, put additional strain on the unit.

How can you tell that the A0285013856 is defective?

A defect shows up as an airbag warning light that stays on permanently or intermittently, as an error message in the instrument cluster, as the diagnostic tool being unable to connect to the control unit, or as a fault memory that cannot be erased. In an emergency, the airbags and seatbelt pretensioners may then fail to trigger.

The airbag warning light in the instrument cluster is the clearest signal. If it stays on permanently or only comes on now and then, have the system checked promptly.

An error message in the instrument cluster confirms the finding. If no connection to the control unit can be established, that also points to a fault. A fault memory that cannot be erased is likewise one of the signs.

Which vehicles is the A0285013856 fitted in?

The A0285013856 is fitted in these vehicles: Mercedes-Benz B-Class W246 (2011-2018).

The suitable models for this part number are listed in the overview below.

• Mercedes-Benz B-Class W246 (2011-2018)

Compare the part number on the label of the removed unit with this page so that you can identify the correct unit. This is not a determination of the cause. Have the fault memory read out beforehand, because the log shows whether the control unit or a plug or cable is the cause.

For the same vehicles, we also repair control units with the part numbers A 246 900 07 09, A246 900 75 02, A2469000809, A2469000903, A2469001003, A2469002313.

How does the repair of the A0285013856 work?

First have the fault memory read out and enclose the log, then disconnect the battery and only then remove the control unit. Next, create a repair order online and send in the well-packed unit. Airbag24 checks it on the test bench, rectifies defects, erases stored crash data and carries out a function test before your own unit is sent back.

This sequence must be followed strictly for safety reasons.

At Airbag24, processing usually takes 3–4 working days. This time covers checking, repairing and testing in-house.

Our repairs come with 2 years' statutory liability for defects. The repaired control unit comes back with all vehicle data and is ready for use as soon as it is refitted — no coding or programming is required.

How does the control unit A0285013856 get to Airbag24?

The unit goes to Airbag24 as a parcel; alternatively, you can arrange a UPS collection for an extra charge. After the repair, Airbag24 sends it back to you by UPS.

Enclose the printed repair order with the parcel and pack the control unit shock-proof.