Airbag control unit with part number A2059004851

What does the airbag control unit A2059004851 do?

The airbag control unit A2059004851 is the central control unit of the restraint system (SRS) for Mercedes-Benz. It processes the signals from the crash sensors and, in an accident, decides within milliseconds which airbags and seatbelt pretensioners are triggered. It monitors the system continuously and reports faults via the airbag warning light.

During operation, the control unit checks the sensors, the firing units and the wiring between them. Only when all parts work together can it activate the correct restraint devices in an emergency.

After an accident, the unit stores crash data and locks itself. This storage is part of how the system works.

Why does the control unit A2059004851 fail?

Stored crash data after an accident is the most common cause for the A2059004851, even if no airbag has deployed; a normal diagnostic tool cannot erase it. Other possible causes include aged electronic components, cold solder joints, moisture and corrosion on plug connections, and voltage spikes.

Crash data is the most obvious suspicion if the unit becomes conspicuous after an accident. However, it is not the only possible explanation.

The other causes relate to ageing, moisture and voltage fluctuations that affect components and connections. Which of them applies only becomes clear once the unit has been tested.

How can you tell that the A2059004851 is defective?

A defect in the A2059004851 shows up as the airbag warning light in the instrument cluster, which may light up permanently or intermittently. Fault messages in the instrument cluster, no connection to the diagnostic tool and a fault memory that cannot be cleared may also occur. In an emergency, airbags and seatbelt pretensioners may then fail to deploy.

Several signs occurring together are a clear reason to have the fault memory read out. The warning light shows that there is a fault, but it does not name the cause.

Which vehicles is the A2059004851 fitted in?

The assignment on this page is based on our data for Mercedes-Benz. The control unit A2059004851 is fitted in these vehicles: Mercedes-Benz C-Class W205 Saloon (2014-2021) and S205 Estate (2014-2021).

You will find the list of vehicles here:

• Mercedes-Benz C-Class W205 Saloon (2014-2021)
• Mercedes-Benz C-Class S205 Estate (2014-2021)

You should compare the part number on the label of the removed unit with this page, because only this confirms that it is the right unit. Have the fault memory read out beforehand, because only this result shows whether the control unit is defective or whether a connector or cable is the cause.

For the same vehicles, we also repair control units with the part numbers A 205 900 21 41, A205 900 18 14, A205 900 63 37, A205 900 95 27, A2059002512, A2059008618.

How does the repair of the A2059004851 work?

Only once the fault memory has been read out and the log is attached do you disconnect the battery and remove the control unit A2059004851. Afterwards, create the repair order online and pack the unit well. At Airbag24, the unit is tested on the test bench, defective components are replaced, stored crash data is erased and the function is tested.

The order of the steps is for safety: the control unit is only removed once the battery has been disconnected.

Processing at Airbag24 usually takes 3–4 working days.

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 A2059004851 get to Airbag24?

You send the control unit A2059004851 as a parcel or book a UPS collection for an extra charge. After the repair, Airbag24 returns it by UPS.

Put the printed repair order into the parcel and pack the unit shock-proof before handing it over.