Airbag control unit with part number A2049012804

What does the airbag control unit A2049012804 do?

The airbag control unit A2049012804 is the central control unit of the restraint system (SRS) for Mercedes-Benz. In an accident, it evaluates the sensor signals and decides which airbags and seatbelt pretensioners are triggered.

The unit monitors the system throughout the entire drive and reports faults to the airbag warning light in the instrument cluster. The decision to trigger is made within a tiny time window that nobody perceives consciously.

After an accident, the control unit stores crash data and locks itself. The lock only ends with a repair.

Why does the control unit A2049012804 fail?

The most common cause is crash data stored after an accident, even if no airbag has deployed. A standard diagnostic tool cannot erase this data. Aged electronics, cold solder joints, moisture and corrosion on plug connections, and voltage spikes are further possible causes.

The crash data is one of the causes that are dealt with first during the repair at Airbag24.

The other causes develop gradually, for example when solder joints give way under temperature changes. Voltage spikes from a weak battery or a jump start are another trigger that is easily overlooked.

How can you tell that the A2049012804 is defective?

A defect in the A2049012804 shows itself through the airbag warning light in the instrument cluster, which lights up permanently or intermittently. Added to this are an error message in the instrument cluster, no connection between the diagnostic tool and the control unit, and a fault memory that cannot be cleared.

These signs belong together and should be considered as a whole. A single symbol is not enough to assess the situation reliably; the combination provides the finding.

In an emergency, airbags and seatbelt pretensioners may fail to deploy while the fault persists. Do not leave the warning unattended.

Which vehicles is the A2049012804 fitted in?

The A2049012804 is fitted in these vehicles: Mercedes-Benz C-Class S204 Estate (2007-2014), W204 Saloon (2007-2014) and C204 Coupé (2011-2015).

The vehicles are summarised in this list:

• Mercedes-Benz C-Class S204 Estate (2007-2014)
• Mercedes-Benz C-Class W204 Saloon (2007-2014)
• Mercedes-Benz C-Class C204 Coupé (2011-2015)

Compare the part number on the label of the removed unit with this page, so that you are sure you have the right unit. Also have the fault memory read out beforehand, because only this result 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 2048709426, 5WK44740, A204 870 68 26, A204 901 26 04, A204 901 35 02, A2048208285.

How does the repair of the A2049012804 work?

First, read out the fault memory and attach the log. Then disconnect the battery, and only after that remove the control unit. Next, create a repair order online and send the unit in well packed.

Airbag24 checks the unit on the test bench, repairs defective components, erases the stored crash data and carries out a function test. Processing at Airbag24 usually takes 3–4 working days. Your own unit is then sent 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 A2049012804 get to Airbag24?

You can send the control unit A2049012804 in as a parcel, or book a UPS collection for an extra charge. After the repair, Airbag24 returns it to you by UPS.

Put the printed repair order in the parcel. Pack the unit so that it is protected against shocks.