Airbag control unit with part number A2129014304

What does the airbag control unit A2129014304 do?

The airbag control unit A2129014304 is the central control unit of the restraint system (SRS) for Mercedes-Benz. It evaluates the signals from the crash sensors and decides in an accident, within milliseconds, which airbags and seatbelt pretensioners are triggered.

The unit monitors the entire system continuously and reports faults via the airbag warning light in the instrument cluster. After an accident it stores crash data and locks itself. Only the repair lifts this lock.

While driving, none of this work is noticeable as long as the system works without faults. The unit checks the connections to sensors and actuators in the background, and exactly this check forms the basis for every message.

Why does the control unit A2129014304 fail?

Stored crash data after an accident is the most common cause of the A2129014304, even if no airbag has deployed. A normal diagnostic tool cannot delete this data. Added to this are aged electronic components, cold solder joints, moisture and corrosion at plug connections, as well as voltage spikes, for example from a weak battery or a jump start.

Airbag24 removes the crash data during the repair, not beforehand. The other causes lie in the electronics themselves or in the connections to the vehicle's electrical system.

How can you tell that the A2129014304 is defective?

A defect on the A2129014304 shows up at the airbag warning light in the instrument cluster, which stays on continuously or at times, at a fault message in the instrument cluster, or at a fault memory that cannot be cleared.

• airbag warning light stays on continuously or at times
• fault message in the instrument cluster
• diagnostic tool cannot establish a connection to the control unit
• fault memory cannot be cleared

Then airbags or seatbelt pretensioners may fail to trigger in an emergency. Therefore have such an indication checked promptly.

Which vehicles is the A2129014304 fitted in?

The airbag control unit A2129014304 is fitted in these vehicles: Mercedes-Benz E-Class S212 Estate (2009-2016), W212 Saloon (2009-2016) and W212 Saloon Facelift (2013-2016).

The vehicles recorded so far for this part number are listed here one below the other:

• 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)

First compare the part number on the label of the removed unit with this page. That only ensures that you have the right unit. Also have the fault memory read out beforehand: only this log shows whether the control unit itself is defective or whether a plug or a 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 A2129014304 work?

First have the fault memory read out and attach the log to the unit. Then disconnect the battery and only then remove the A2129014304. Next create a repair order online and send in the well-packed unit.

Airbag24 checks the unit on the test bench, replaces defective components, deletes the stored crash data and carries out a function test. The unit then goes back to you.

Processing at Airbag24 usually takes 3–4 working days; this time covers only checking, repairing and testing. 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 A2129014304 get to Airbag24?

You send in the A2129014304 as a parcel or book a UPS collection for an extra charge. After the repair Airbag24 sends the unit back to you by UPS.

Put the printed repair order into the parcel and pack the control unit shockproof. The choice of shipping method does not change the course of the repair.