Airbag control unit with part number A4479000900

What is the function of the airbag control unit A4479000900?

The control unit A4479000900 is the central airbag/SRS module for the Mercedes-Benz V-Class and Vito of the W447 series. Its primary task is to monitor crash sensors, evaluate impact data in real time, and, when necessary, activate relevant restraint systems such as airbags and seatbelt pretensioners to protect occupants.

As the heart of the passive safety system, this module continuously communicates with all connected sensors and actuators. It processes signals from acceleration and pressure sensors to determine the severity and type of a collision.

Based on this data, it makes the critical decision about which airbags (front, side, head) and which seatbelt pretensioners should be deployed to ensure maximum protection for vehicle occupants.

What defects occur in A4479000900?

The most common reason for repairing A4479000900 is stored crash data following an accident, which prevents the module from functioning properly. In addition, internal electronic faults—such as defective components on the circuit board (e.g., voltage regulators, capacitors), damage caused by overvoltage, or interrupted communication—are typical hardware-related failure causes.

After a collision, the control unit deliberately stores “crash data” or “impact data.” This entry serves as a permanent record of the event and locks the module out of further use, indicated by the airbag warning light. Repair involves the professional and verifiable deletion of this data.

Another frequent cause is internal hardware failure. This includes defects in electronic components such as SMD resistors, transistors, or voltage regulators, often resulting from voltage spikes or material fatigue. Such failures can lead to complete loss of communication or specific internal error codes.

When searching for replacement parts, it’s helpful to know that alternative part numbers A4479001000 or A4479004908 can also be used for comparable modules. However, repairing the original unit is often the simplest solution.

How do you recognize a defect in the A4479000900 control unit?

A defect in the A4479000900 control unit is most clearly indicated by a permanently or intermittently illuminated airbag warning light on the instrument cluster. Another key symptom is the inability of a diagnostic tool to establish communication with the SRS module, making it impossible to read fault codes.

The most prominent and unmistakable sign is the active airbag warning light. It does not turn off after starting the engine, signaling a critical fault in the passive safety system that requires immediate inspection.

In workshop practice, the defect often manifests as a complete loss of communication. The diagnostic tool cannot access the control unit via the OBD-II interface or reports implausible or non-erasable internal error codes.

In which vehicles is A4479000900 installed?

The airbag control unit A4479000900 is specifically used in vehicles of the Mercedes-Benz W447 series. At Airbag24, we repair this module for the Mercedes-Benz V-Class (from 2014 onward) as well as the technically related Mercedes-Benz Vito (from 2014 onward), covering all variants within these model lines.

At Airbag24, we specialize in repairing part number A4479000900 for the following specific models:

Mercedes-Benz: V-Class (W447 series, from model year 2014)

Mercedes-Benz: Vito (W447 series, from model year 2014)

How is the A4479000900 control unit professionally repaired?

Professional repair of A4479000900 at Airbag24 begins with a comprehensive initial analysis to read the fault memory. Depending on the nature of the fault, either the stored crash data is reset or defective electronic components on the circuit board are replaced at the component level. A final functional test ensures full operability.

After submitting the control unit to Airbag24, a detailed incoming inspection takes place. Using specialized diagnostic equipment, the fault memory is read to precisely identify the root cause—whether it’s stored crash data or an internal electronic fault.

If crash data is present, it is professionally and transparently reset. If an electronic fault is detected, repairs are carried out at the component level, including replacing faulty components such as resistors, capacitors, or processors, as well as inspecting and reworking cold solder joints.

Finally, a thorough functional test is performed on the test bench to confirm correct communication and full operational readiness of the control unit. We provide 2 years' statutory liability for defects on every repair performed.