Airbag control unit with part number A2129010800

What does the airbag control unit A2129010800 do?

The airbag control unit A2129010800 is the central control unit of the SRS in Mercedes-Benz. It evaluates the crash sensors, decides in an accident whether airbags and seatbelt pretensioners are triggered, and shows faults via the airbag warning light.

After an accident, the unit stores crash data and locks itself.

It works in the background, because in an emergency all components must work together.

Why does the control unit A2129010800 fail?

With the A2129010800, stored crash data is the most common cause of a defect, even if no airbag has deployed. A normal diagnostic tool cannot delete it. Other causes are aged components, cold solder joints, moisture and corrosion at plugs, and voltage spikes.

Airbag24 removes the crash data during the repair.

The other causes at a glance:

• Aged electronic components
• Cold solder joints
• Moisture and corrosion at plug connections
• Voltage spikes, for example from a weak battery or jump-starting

Which of these applies is shown only by the evaluation of the fault memory and the check that follows.

How can you tell that the A2129010800 is defective?

A defect on the A2129010800 shows up as the airbag warning light, as fault messages or as a missing connection to the diagnostic tool. In an emergency, airbags and seatbelt pretensioners may then fail to deploy.

Typical signs are:

• The airbag warning light in the instrument cluster stays on permanently.
• The airbag warning light lights up intermittently.
• A fault message appears in the instrument cluster.
• The diagnostic tool cannot reach the control unit.
• The fault memory cannot be cleared.

The warning light is a message from the system itself and not a minor matter.

Which vehicles is the A2129010800 fitted in?

The airbag control unit A2129010800 is fitted in these vehicles: Mercedes-Benz E-Class S212 Estate (2009-2016), W212 Saloon (2009-2016) and W212 Saloon Facelift (2013-2016).

The list of assigned vehicles follows:

• 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 with this page only ensures that you have removed the right unit. Have the fault memory read out beforehand. Only this result decides 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 A2129010800 work?

For the A2129010800, this sequence applies: first read out the fault memory and enclose the log, then disconnect the battery, afterwards remove the control unit and create the repair order online. Processing at Airbag24 usually takes 3–4 working days.

Airbag24 checks the unit on the test bench, replaces defective components where required, deletes stored crash data and carries out a functional test. Your own unit is then 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 A2129010800 get to Airbag24?

The control unit A2129010800 is either sent in as a parcel or collected by UPS for an extra charge; after the repair it comes back by UPS.

Put the printed repair order into the parcel and pack the unit shockproof.