Airbag control unit with part number A2129018801

What does the airbag control unit A2129018801 do?

The airbag control unit A2129018801 is the central control unit of the restraint system (SRS) of Mercedes-Benz. It evaluates the signals from the crash sensors and decides in a crash, within milliseconds, which airbags and seatbelt pretensioners are triggered. At the same time it monitors the system continuously.

The unit reports faults via the airbag warning light in the instrument cluster. After an accident it stores crash data and locks itself.

It is precisely the combination of detecting, deciding and reporting that makes this control unit the core of the safety technology in the vehicle.

Why does the control unit A2129018801 fail?

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

Crash data remains in the memory until it is removed during the repair. Airbag24 deletes it, because an ordinary diagnostic tool is not capable of doing so.

The other causes concern the electronics themselves and their connections. A damp or corroded contact can cause dropouts, and a voltage spike loads components that are designed for steady voltage.

How can you tell that the A2129018801 is defective?

The airbag warning light in the instrument cluster lights up continuously or intermittently, an error message appears in the instrument cluster, the diagnostic tool gets no connection to the control unit, and the fault memory cannot be cleared.

The warning light shows the fault, and that is exactly how you recognise it. As long as the control unit is faulty, airbags and seatbelt pretensioners may not be able to trigger in an emergency.

If you see these signs, have the fault memory read out promptly rather than waiting for a further hint.

Which vehicles is the A2129018801 fitted in?

The following assignment applies to exactly this part number. The airbag control unit A2129018801 is installed in these vehicles: Mercedes-Benz E-Class S212 Estate (2009-2016), W212 Saloon (2009-2016) and W212 Saloon Facelift (2013-2016).

The vehicles this part number applies to are listed one below the other here.

• Mercedes-Benz E-Class S212 Estate (2009-2016)
• Mercedes-Benz E-Class W212 Saloon (2009-2016)
• Mercedes-Benz E-Class W212 Saloon Facelift (2013-2016)

Compare the part number on the label of the removed unit with this page; this ensures that you have the right unit in front of you. Also have the fault memory read out before taking further steps: only this log shows whether the control unit is defective or whether a plug or cable is the cause.

For the same vehicles, we also repair control units with the part numbers 2129011105, A212 901 42 04, A212 901 85 08, A2128603002, A2129010700.

How does the repair of the A2129018801 work?

First have the fault memory read out and attach the log. Then disconnect the battery and only afterwards remove the control unit. Then create a repair order online and send the well-packed unit in.

Airbag24 checks the unit on the test bench and replaces defective components. Then the stored crash data is deleted, a function test follows, and your own unit is sent back to you. Airbag24 needs 3–4 working days in total for testing, repair and function test.

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 A2129018801 get to Airbag24?

You send the unit as a parcel or book a UPS collection for an extra charge. After the repair, Airbag24 sends your own unit back to you by UPS. Enclose the printed repair order and pack the unit shock-proof.

Whether you ship it yourself or use the collection, the parcel needs sturdy packaging and the order inside the box.