Airbag control unit with part number A2139004325

What does the airbag control unit A2139004325 do?

The airbag control unit A2139004325 is the central evaluation unit of the restraint system (SRS) in the Mercedes-Benz. It processes the signals from the crash sensors and, in the event of an accident, decides within milliseconds whether airbags and seatbelt pretensioners are triggered. It also monitors the system continuously and reports faults via the airbag warning light.

After an accident it stores crash data and locks itself.

In everyday use the unit remains inconspicuous. Only when it detects a deviation does a message appear in the instrument cluster.

Why does the control unit A2139004325 fail?

Stored crash data is the most common cause, even if no airbag was deployed in the accident. It cannot be removed with a normal diagnostic tool. Other causes include ageing electronics, cold solder joints, moisture and corrosion at the plug connections, and voltage spikes, for example from a weak battery or a jump start.

Crash data is created because the unit has registered an event as an accident. The trigger is the detection of the event, not the firing of an airbag.

The remaining causes relate to the electronics and their connections. Components age, and moisture can attack the contacts, so the control unit reports a fault.

Voltage spikes occur mainly with a weak battery or when starting with external power. They can also affect the electronics.

How can you tell that the A2139004325 is defective?

The airbag warning light in the instrument cluster lights up constantly or only intermittently, and an error message appears. The diagnostic tool cannot establish a connection to the control unit, and the fault memory cannot be cleared.

These signs mean that the system has registered a fault. In an emergency, airbags and seatbelt pretensioners may fail to deploy while the fault persists. Do not leave the system running unattended; have it checked promptly.

Which vehicles is the A2139004325 fitted in?

The A2139004325 is fitted in these vehicles: Mercedes-Benz E-Class S213 Estate (2016-2023) and W213 Saloon (2016-2023).

The list contains the vehicles stored for this control unit.

• Mercedes-Benz E-Class S213 Estate (2016-2023)
• Mercedes-Benz E-Class W213 Saloon (2016-2023)

Comparing the part number on the label of the removed unit with this page only shows that it is the right unit. Before that, have the fault memory read out, because only the log shows whether the control unit itself is defective or whether a plug or cable is the cause.

For the same vehicles, we also repair control units with the part numbers A213 900 46 25, A213 900 88 22, A213 900 88 28, A2139007105, A2139010104.

How does the repair of the A2139004325 work?

First, have the fault memory read out and enclose the log. Then disconnect the battery and only then remove the control unit. Next, create a repair order online and send the unit well packed. Processing at Airbag24 usually takes 3–4 working days.

Airbag24 tests the unit on the test bench, repairs defective components, deletes the stored crash data and carries out a 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 A2139004325 get to Airbag24?

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

The printed repair order goes in the parcel, and the unit must be packed shock-proof.