Airbag control unit with part number A1779000404

What does the airbag control unit A1779000404 do?

The airbag control unit A1779000404 is the central control unit of the restraint system (SRS) for Mercedes-Benz. It evaluates the signals of the crash sensors, decides in an accident within fractions of a second on airbags and seatbelt pretensioners, and monitors the system continuously.

In addition to the part number, the housing carries the number Bosch 0285015020.

The unit reports faults via the airbag warning light in the instrument cluster. After an accident it stores crash data and locks itself.

Why does the control unit A1779000404 fail?

The most common cause is stored crash data after an accident, even if no airbag has fired. A normal diagnostic tool does not erase it. Aged components, cold solder joints, moisture or voltage spikes can also cause the control unit A1779000404 to fail.

Erasing the crash data is part of the repair at Airbag24.

Aged electronics and cold solder joints impair the function. Moisture and corrosion at plug connections, as well as voltage spikes, for example from a weak battery or jump-starting, can cause problems too.

How can you tell that the A1779000404 is defective?

A defect on the A1779000404 shows primarily on the airbag warning light in the instrument cluster. Further signs follow that you notice directly in the vehicle or on the diagnostic tool.

• airbag warning light in the instrument cluster lights permanently or intermittently
• fault message in the instrument cluster
• diagnostic tool receives no connection to the control unit
• fault memory cannot be erased

Such a finding means that airbags and seatbelt pretensioners may possibly not deploy in an emergency. A prompt check is therefore advisable.

Which vehicles is the A1779000404 fitted in?

The control unit A1779000404 is fitted in these vehicles: Mercedes-Benz A-Class W177 (from 2018).

The vehicles in detail:

• Mercedes-Benz A-Class W177 (from 2018)

Before removal, compare the part number on the label with this page. This shows whether you are removing the correct unit, but it does not clear up the cause of the fault. The fault memory must be read out beforehand, because only it shows whether the control unit is defective or a plug or cable is responsible.

For the same vehicles, we also repair control units with the part numbers 0 285 015 019, 0285020871, A 177 900 03 04, A1779027906, A2479013703, A2479018801.

How does the repair of the A1779000404 work?

First read out the fault memory and enclose the log, then disconnect the battery and only then remove the control unit A1779000404. Afterwards create a repair order online and send the well-packed unit. Processing at Airbag24 usually takes 3–4 working days.

Airbag24 checks the unit on the test bench, repairs the defective components, erases the stored crash data and carries out a functional test. Your unit then goes back 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 A1779000404 get to Airbag24?

You send the control unit A1779000404 as a parcel or book a UPS collection for an extra charge. After the repair, Airbag24 sends it back to you by UPS.

Put the printed repair order into the parcel and pack the unit shock-proof.