Airbag control unit with part number 5WK43749

What is the function of Airbag Control Unit 5WK43749?

The Airbag Control Unit 5WK43749, often identified by the alternative OEM part number 8K0959655B, serves as the central control unit for the entire occupant safety system (SRS) in certain Audi models. It processes data from crash sensors and determines whether and when airbags and seatbelt pretensioners should be deployed. Additionally, it stores accident-related data (crash data).

As the brain of the safety system, this component continuously monitors all connected sensors and actuators—from the acceleration sensors at the front of the vehicle to the seat occupancy detectors. In the event of a collision, the unit analyzes incoming signals within milliseconds and activates the necessary restraint systems to provide optimal protection for occupants.

Following an accident or in case of an internal fault, the control unit often locks the system and illuminates the warning light to indicate the need for inspection. Proper functionality is therefore essential for vehicle safety and passing the main inspection (TÜV).

Why does Airbag Control Unit 5WK43749 fail?

The most common causes of failure for the 5WK43749 control unit are internal electronic malfunctions, stored crash data after an accident, or external factors such as undervoltage and moisture. A defect can also occur spontaneously, even without a crash, indicating wear on electronic components.

A key reason for malfunction is an internal electronics error, which may result from short circuits, defective components on the circuit board, or issues with the internal memory. Such faults often trigger error codes 65535 or B200049 (control unit defective).

After a crash, the control unit stores so‑called crash data. This storage is a safety measure that permanently disables the airbag system, even if mechanical damage to the vehicle has been repaired. The airbag warning light remains illuminated until the data is professionally reset.

External influences—such as a weak or faulty vehicle battery, a malfunctioning alternator, or broken wiring—can lead to undervoltage and damage the control unit’s sensitive electronics. Similarly, moisture, for example from spilled beverages near the seats, can cause corrosion and short circuits.

How do you recognize a defect in Control Unit 5WK43749?

A defective 5WK43749 airbag control unit typically manifests as a permanently or intermittently illuminated airbag or SRS warning light on the instrument cluster. Other reliable indicators include loss of communication with the diagnostic tool and persistent error codes such as 65535, B200049, or 10485833, which directly point to an internal fault.

The most obvious symptom is the active airbag warning light, signaling a problem in the occupant protection system and preventing the vehicle from passing the main inspection. In this state, the system is non‑functional.

Another clear sign is when a workshop using an OBD diagnostic device cannot establish communication with the airbag control unit. The unit no longer responds to requests, making precise fault analysis impossible.

If error codes like 65535 (control unit defective), B200049 (control unit defective/internal electronics fault), or A00049-89 are read and cannot be cleared, this is a definitive indication of a hardware defect within the control unit itself.

Caution: Using airbag simulators or resistors to bypass the system is life‑threatening and illegal. Such manipulations falsely suggest a functioning system while disabling critical safety features and resulting in the revocation of operating approval.

In which vehicles is Control Unit 5WK43749 installed?

The Airbag Control Unit 5WK43749 is primarily installed in various Audi models. It is commonly found in A4, A5, and RS5 series vehicles. At Airbag24, we repair this control unit for the specific vehicle models and series listed here.

At Airbag24, we offer professional repair services for the control unit with part number 5WK43749 (and reference number 8K0959655B) for the following Audi models:

Audi A4: 8W

Audi A5: 8TA Sportback (2007–2011), 8TA Sportback Facelift (2011–2016)

Audi RS5: 8T (2010–2012), 8T Facelift (2012–2015)

If your vehicle model is not listed exactly, please contact us. Often there are overlaps or variants that can also be repaired.

How does the repair of 5WK43749 proceed at Airbag24?

After sending your removed control unit to Airbag24, our technicians perform a comprehensive electronic analysis. The repair includes resetting stored crash data, reprogramming the memory, and replacing defective components to restore full functionality. We provide 2 years' statutory liability for defects on every repair.

First, a diagnostic should be performed at the workshop to confirm that the fault indeed lies in the control unit. After proper removal, please send the unit to us securely packaged.

At Airbag24, repairs follow a proven process. Specialized technicians analyze the circuit board and internal memory. Stored crash data is completely erased, and the unit is restored to its factory settings. If a hardware defect is detected, the damaged electronic components are professionally replaced.

Following successful repair and final testing, the control unit is returned to you. It is fully functional again immediately after installation (plug-and-play). If necessary, the vehicle’s fault memory may need to be cleared once more.