Airbag control unit with part number A2049012704

What is the function of the airbag control unit A2049012704?

The airbag control unit A2049012704, also known as the SRS control unit, is the central control module for the occupant protection system in various Mercedes-Benz models. It processes data from crash sensors and determines whether to deploy airbags and seatbelt pretensioners, ensuring passenger safety in the event of a collision.

As the brain of the passive safety system, this control unit continuously evaluates signals from acceleration and pressure sensors in the vehicle. In the event of a collision, it calculates the severity of the impact within milliseconds and activates the necessary restraint systems, such as front, side, or head airbags, as well as seatbelt pretensioners.

After deployment, the A2049012704 unit stores so‑called crash data. This storage serves as a safety measure: the control unit locks itself, preventing reuse without professional repair to ensure the full functionality of the safety system.

Why does the A2049012704 control unit fail?

The most common cause of failure for the A2049012704 control unit is the retention of crash data after an accident, which blocks further operation. Other typical causes include internal electronic faults, faulty power supply, or component damage, often indicated by persistent error codes such as B220700 or B220800.

The most frequent issue is blockage due to stored crash data. This is not a conventional defect but rather a manufacturer‑imposed lock triggered after a crash. Such data generally cannot be erased using standard workshop diagnostic tools.

Electronic malfunctions on the circuit board are another common source of problems. Error codes like A10E (faulty power supply), B220700, or B220800 (internal fault) directly point to hardware defects inside the unit. Additionally, missing chassis numbers in memory may also indicate such internal failures.

This control unit is also known under alternative part numbers 5WK44739, A2049012604, and 5WK44740. The fault patterns and repair approaches are often identical across these variants.

How do you recognize a defect in the A2049012704?

A defective A2049012704 airbag control unit primarily manifests as a permanently illuminated airbag or SRS warning light on the instrument cluster. Communication with the diagnostic tool may also be impossible, or specific, non‑erasable error codes such as “internal fault” or “faulty power supply” appear.

The most obvious symptom is the persistently lit SRS indicator light. This poses a critical safety risk, as the entire airbag system becomes disabled in case of a fault and will not deploy during a crash. Furthermore, a vehicle with a lit airbag warning light will fail the main inspection (TÜV).

Another clear sign is when the workshop’s diagnostic equipment cannot establish communication with the airbag control unit. The device fails to respond to diagnostic requests, making precise fault analysis difficult and often indicating a power supply issue or a complete internal failure.

In addition, the display may show error messages such as “airbags defective,” “side sensor error,” or “fuel shut-off valve malfunction.” Before removing the control unit, it is essential to have a qualified workshop verify that the problem does not stem from external components, such as the seat occupancy mat.

In which vehicles is the A2049012704 installed?

The A2049012704 airbag control unit is fitted in specific Mercedes-Benz model series. At Airbag24, we repair this control unit for the C-Class of generation 204 (sedan, estate, coupe) as well as for the GLK SUV of the X204 series from the corresponding model years.

At Airbag24, we have successfully refurbished this control unit for the following Mercedes-Benz models:

Mercedes-Benz C-Class W204 sedan (2007–2014) Mercedes-Benz C-Class S204 estate (2007–2014) Mercedes-Benz C-Class C204 coupe (2011–2015) Mercedes-Benz GLK-Class X204 SUV (2008–2015)

Accurate matching is crucial for the proper functioning of the safety system. Always compare the part number on your removed control unit with the specified number A2049012704.

How does Airbag24 repair the A2049012704?

At Airbag24, repairing the A2049012704 control unit follows a certified process. After removal and submission, our technicians analyze the unit, fix internal faults, repair the power supply, and erase stored crash data. We provide 2 years' statutory liability for defects on every repair.

First, have a qualified workshop read out the fault memory to confirm that the issue indeed lies with the control unit. After professional removal, pack the unit securely for transport and send it to us. Including a diagnostic report will expedite the analysis.

Upon receipt at Airbag24, specialized technicians perform a thorough inspection. The repair includes correcting internal electronic faults, restoring the power supply, and safely erasing crash data. The control unit is then reprogrammed and tested for full functionality.

Following successful repair and final inspection, we return the control unit to you. After reinstalling it in your vehicle, you may need to clear the vehicle’s overall fault memory in some cases. All our repairs come with 2 years' statutory liability for defects.