Airbag control unit with part number A2129011305

What does the airbag control unit A2129011305 do?

The airbag control unit A2129011305 is the central control unit of the restraint system (SRS) in the Mercedes-Benz. It processes the signals from the crash sensors, selects the appropriate airbags and seatbelt pretensioners in an accident, and monitors the system continuously.

If the unit detects a fault, the airbag warning light in the instrument cluster comes on. This way, as the driver, you learn straight away that something is wrong in the restraint system.

After an accident, the control unit stores crash data and locks itself. Only the repair lifts the lock.

Why does the control unit A2129011305 fail?

The most common cause is an entry with crash data that remains in the unit after an accident, even without a triggered airbag. A standard diagnostic tool cannot reach this data. Other causes are aged components, moisture, cold solder joints and voltage spikes.

Airbag24 removes the crash data as part of the repair, because without this step the entry would remain in the unit.

Typical further triggers are:

• aged electronic components
• cold solder joints
• moisture and corrosion at plug connections
• voltage spikes, for example with a weak battery or jump leads

How can you tell that the A2129011305 is defective?

The airbag warning light in the instrument cluster lights up permanently or intermittently, and a fault message in the instrument cluster may appear as well. In addition, the diagnostic tool cannot establish a connection to the control unit, and the fault memory cannot be cleared.

In an emergency, airbags and seatbelt pretensioners may then fail to deploy. Have the cause clarified promptly.

Which vehicles is the A2129011305 fitted in?

The A2129011305 is fitted in these vehicles: Mercedes-Benz E-Class S212 Estate (2009-2016), W212 Saloon (2009-2016) and W212 Saloon Facelift (2013-2016).

The models in which this part number is used are listed below:

• 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)

Comparing the part number on the label of the removed unit with this page only confirms that it is the right unit. Have the fault memory read out beforehand, because 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 A2129011305 work?

First have the fault memory read out, attach the log and then disconnect the battery; only then remove the control unit. Afterwards, create a repair order online and send in the well-packed unit. Processing at Airbag24 takes 3–4 working days.

At Airbag24 the unit is checked on the test bench. Defective components are replaced, crash data is erased and a function test is finally carried out.

Afterwards your own unit is returned to you. 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 A2129011305 get to Airbag24?

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

The printed repair order and a shock-proof protective cover for the unit belong in the parcel.