Airbag control unit with part number A2129017902

What does the airbag control unit A2129017902 do?

The airbag control unit A2129017902 manages the SRS restraint system of Mercedes-Benz in the vehicle. If an accident is detected, it processes the signals from the crash sensors and determines within milliseconds which airbags and seatbelt pretensioners are triggered. After an accident, it stores crash data and locks itself.

In operation, the unit monitors the system without interruption. If it detects a fault, it indicates this via the airbag warning light in the instrument cluster.

Why does the control unit A2129017902 fail?

The most common cause: crash data stored on the control unit A2129017902 after an accident, even if no airbag has fired. Other causes include aged electronics, cold solder joints, moisture and corrosion on plug connections, and voltage spikes.

Crash data remains in memory after an accident, even if no airbag fires. A diagnostic tool from normal workshop use cannot delete it; it only disappears with the repair.

Aged electronics, cold solder joints and corrosion on plug connections are also among the causes to consider. Voltage spikes from a weak battery or a jump start put additional strain on the electronics. The fault memory shows which of these points applies.

How can you tell that the A2129017902 is defective?

If the airbag warning light in the instrument cluster is on permanently or intermittently, the control unit A2129017902 has a fault. An error message appears alongside it, the diagnostic tool finds no connection, and the fault memory cannot be cleared.

In an emergency, airbags and seatbelt pretensioners may then fail to deploy. The condition therefore requires a prompt check.

Even if the car is still driving, the warning remains valid. If there is no contact with the diagnostic tool, this indicates disrupted communication, which can only be narrowed down with the fault memory.

Which vehicles is the A2129017902 fitted in?

The control unit A2129017902 is in use in these vehicles: Mercedes-Benz E-Class S212 Estate (2009-2016), W212 Saloon (2009-2016) and W212 Saloon Facelift (2013-2016).

The vehicles in detail:

• 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)

A comparison of the part number on the label with this page confirms that you have the right unit. This comparison does not show the cause of the defect. Therefore have the fault memory read out before removal. 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 2129011105, A212 901 42 04, A212 901 85 08, A2128603002, A2129010700.

How does the repair of the A2129017902 work?

First have the fault memory read out and enclose the log. Then disconnect the battery and only afterwards remove the control unit A2129017902. Create the repair order online and send in the well-packed unit. Airbag24 needs 3–4 working days as a rule for checking, repairing and testing.

The sequence is mandatory for safety reasons. At Airbag24, the unit is checked, defective components are replaced, crash data is deleted and a function test concludes the work.

Your own unit is returned to you afterwards.

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 A2129017902 get to Airbag24?

You can send the A2129017902 unit to Airbag24 as a parcel, or book a UPS collection for an extra charge. The return journey after the repair is also made by UPS.

The printed repair order goes in the parcel. Pack the control unit shockproof.