Airbag control unit with part number 8K0 959 655 P

What is the function of Airbag Control Unit 8K0 959 655 P?

The airbag control unit with part number 8K0 959 655 P is the central control module for the occupant protection system, primarily installed in the Audi A5 8T. It analyzes data from crash sensors and, in the event of an accident, deploys airbags, seatbelt pretensioners, and, if applicable, the rollover bar to protect vehicle occupants.

As the “brain” of the safety system, it interprets signals from acceleration and pressure sensors within the vehicle. Based on this data, the unit determines within milliseconds which restraint systems need to be activated. After deployment, it stores relevant crash data, which prevents further operation without professional reprogramming.

Why does control unit 8K0 959 655 P fail?

A failure of control unit 8K0 959 655 P is usually caused by stored crash data following an accident that cannot be erased. Other common causes include external factors such as moisture, excessive heat, or electrical issues in the vehicle’s electrical system—such as a battery short circuit.

The most frequent cause is the retention of crash data after restraint systems like the knee airbag or rollover bar have been deployed. For safety reasons, this data locks the control unit and cannot be cleared by standard workshop diagnostic tools. Repair is essential to restore full functionality.

Hardware defects on the circuit board are also prevalent. These can result from moisture ingress, thermal overload, or voltage fluctuations in the vehicle’s electrical system. Such faults often lead to internal malfunctions or complete communication failure.

Typical error codes indicating a defect include 65535 (control unit defective), B200049, or A00049-89. These point to an internal, non‑erasable fault. In some cases, software errors or coding problems may also occur.

This control unit is also known under similar part numbers, such as the generic designation 8K0 959 655, or specific variants like 8K0959655J, 5WK43748, and 5WK43749. Checking compatibility before repair is advisable.

How do you recognize a defect in control unit 8K0 959 655 P?

A defect in control unit 8K0 959 655 P typically manifests as a permanently illuminated or intermittently flashing airbag warning light on the instrument cluster. Often, no communication can be established with the control unit via a diagnostic tool, complicating troubleshooting.

The most obvious sign is the active airbag warning light, which indicates a fault in the restraint system and persists even after restarting the engine. This is a safety‑critical issue that requires immediate attention.

Another clear symptom is the loss of diagnostic capability. If the workshop detects a “no communication” entry in the fault memory, this strongly suggests a severe internal defect within the control unit itself.

In addition, secondary symptoms may appear in the vehicle. Customers report other malfunctions, such as a faulty clock, ignition problems, or a blinking engine check light—all potentially linked to a defect in the airbag control unit.

In which vehicles is control unit 8K0 959 655 P installed?

The airbag control unit with part number 8K0 959 655 P is specifically designed for Audi models. It is mainly used in the Audi A5 of the 8T series and the Audi S5, both in original versions and facelifted models.

At Airbag24, we repair this control unit for the following Audi models:

Audi A5 8T (model years 2007–2011)Audi A5 8T Facelift (model years 2011–2016)Audi S5 8T (model years 2007–2016)

Since there are several variants, it is crucial to carefully verify the part number before removal to ensure proper matching.

How does the repair of 8K0 959 655 P proceed at Airbag24?

Repair at Airbag24 begins with a professional diagnosis of the submitted control unit. This is followed by electronic refurbishment, during which defective components are replaced, the software is reprogrammed, and, most importantly, all stored crash data is completely erased. Finally, the unit undergoes a full functional test as if it were new.

Once the defective control unit arrives at Airbag24, our technicians conduct a thorough analysis to identify the root cause of the fault. The repair process includes replacing faulty components on the circuit board, reprogramming the memory, and fully resetting all error codes and crash records. Following successful restoration, the unit undergoes comprehensive functional testing. We provide 2 years' statutory liability for defects on every repair.