Airbag control unit with part number 4M0959655B

What is the function of the airbag control unit 4M0959655B?

The airbag control unit with part number 4M0959655B is the central control unit for the entire occupant safety system (SRS) in vehicles such as the Audi SQ7, Q7, and Q8 from the 4M series. It receives data from crash sensors, processes this information in real time, and controls the activation of airbags and seatbelt pretensioners.

As the brain of the passive safety system, this control unit is responsible for coordinating life-saving restraint systems in the event of a collision. It continuously analyzes signals from acceleration and pressure sensors distributed throughout the vehicle.

Based on the severity and type of impact, the device determines within milliseconds which airbags (front, side, head) and seatbelt pretensioners need to be deployed to provide optimal protection for occupants. Therefore, flawless functionality is essential for vehicle safety.

Why does the control unit 4M0959655B fail?

The most common cause of malfunction in the control unit 4M0959655B is the storage of crash data following an accident or a serious fault condition. Although the hardware itself is often intact, this stored data prevents normal operation and triggers the airbag warning light. Other potential causes include communication issues.

After a triggering event—whether an actual accident or a severe system error—the control unit writes a permanent fault entry into its internal memory. This lock, known as “crash data,” serves as a safety measure that necessitates a full system check.

While technical diagnostics also consider factors such as software errors, CAN bus communication problems, or coding issues, the primary reason for a persistently illuminated warning light is usually the stored crash data.

In this context, related part numbers 4KE959655B and 4KE959655L are also relevant for repairs and replacements, as they may be used in the same vehicle platforms.

How do you recognize a defect in the 4M0959655B?

A defect in the airbag control unit 4M0959655B primarily manifests as a permanently illuminated airbag warning light on the instrument cluster. Additionally, the control unit may become unresponsive to diagnostic tools and cease all communication. In the worst-case scenario, this can lead to complete failure of the safety system.

The most obvious sign is the activated red airbag or SRS warning light on the dashboard. It does not turn off after starting the vehicle, indicating a persistent, safety-critical system error.

Another clear symptom appears in the workshop: the control unit no longer responds to diagnostic requests. When a technician attempts to read the fault memory, communication fails, making precise fault analysis impossible without removing the unit.

The most serious consequence is the potential total failure of the occupant protection system. In the event of an accident, airbags and seatbelt pretensioners would not deploy, posing a significant safety risk.

In which vehicles is the control unit 4M0959655B installed?

The airbag control unit 4M0959655B is specifically designed for Audi’s larger SUV models built on the 4M platform. These include, above all, the Audi Q7 4M and the Audi Q8 4M. It is also prominently used in the performance-oriented Audi SQ7 4M, both in its first generation and in the facelifted model.

At Airbag24, we repair the control unit with part number 4M0959655B and its functionally related variants for the following specific Audi models:

Audi SQ7 4M (model years 2016–2019)

Audi SQ7 4M Facelift (from model year 2019 onward)

Audi Q7 4M

Audi Q8 4M

How is the control unit 4M0959655B professionally repaired?

Professional repair of the control unit 4M0959655B at Airbag24 focuses, after a comprehensive diagnosis, on eliminating the root cause of the fault. In most cases, the stored crash data is safely and completely erased. The unit then undergoes a functional test and is returned ready for installation.

Upon submission to Airbag24, the control unit follows a standardized repair process. First comes an initial assessment, during which communication with the device is checked and the internal fault memory is read to verify the exact cause.

The core of the restoration is the proper deletion of stored crash data from the control unit’s memory. This process returns the device to its pre-failure state, restoring full functionality without requiring an expensive new part.

Finally, each repaired control unit is tested on a specialized test bench to simulate the proper functioning of all systems and ensure it communicates flawlessly with the vehicle once again. We provide 2 years' statutory liability for defects on every repair.