Airbag control unit with part number 8K0 959 655 K

What is the function of the airbag control unit 8K0 959 655 K?

The control unit with part number 8K0 959 655 K is the central control module for the occupant restraint system (SRS) in various Audi models. It continuously analyzes data from acceleration and seatbelt force sensors to precisely and rapidly deploy airbags and pretensioners in the event of a crash, thereby ensuring the safety of vehicle occupants.

As the “brain” of the entire restraint system, this module—primarily installed in the Audi B8/8T platform (e.g., A4, A5)—is responsible for monitoring all safety‑related components, including airbags, seatbelt pretensioners, and their associated sensors.

Under normal operating conditions, the control unit constantly receives and processes signals from crash sensors. In the event of a collision, it evaluates the incoming data within milliseconds to determine whether and which restraint systems need to be activated to provide optimal protection for occupants.

In addition, it communicates with other vehicle control units via the CAN and LIN buses to exchange relevant vehicle data and signal malfunctions on the instrument cluster.

Typical Defects and Causes of Failure for 8K0 959 655 K

The most common cause of failure for the 8K0 959 655 K control unit is the storage of crash data after an accident, which locks the system. Other frequent issues include electronic faults on the circuit board, such as defective components, damaged solder joints, communication disruptions, or memory errors in the internal memory chip.

Even after minor collisions, so‑called crash or event data are stored in the control unit’s internal memory. These records permanently lock the system, preventing the airbag warning light from being cleared. Professional reset procedures are therefore essential.

Another common problem involves electronic defects on the main circuit board. This may manifest as individual components—such as capacitors or resistors—exceeding their tolerance limits, or as hairline cracks in solder joints leading to sporadic failures. Such thermal issues are particularly likely to occur during temperature fluctuations.

Communication errors on the CAN or LIN bus are also a well‑known cause. In these cases, the control unit can no longer communicate with the diagnostic tester or other vehicle components, often due to a malfunction in the relevant transmitting or receiving circuitry on the board.

These defects affect the entire model series, including variants with different final letters, such as 8K0 959 655 N, as well as alternative Bosch part numbers like 5WK43748 and 5WK43749. The underlying causes are typically identical.

Symptoms of a Faulty Airbag Control Unit 8K0 959 655 K

A defect in the 8K0 959 655 K control unit primarily manifests as a continuously illuminated or intermittently flashing airbag warning light on the instrument cluster. Communication with the control unit via a diagnostic tool may also be lost, or persistent, non‑erasable fault codes may be stored.

The most obvious sign is the activated airbag indicator light. After starting the vehicle, the system performs a self‑diagnostic check; if an internal fault is detected, the warning light remains on to alert the driver to a malfunction in the safety system.

Another clear symptom is the lack of response from the control unit during a diagnostic query. In such cases, the workshop cannot establish a connection to read out the fault memory, indicating either a complete breakdown of the communication module or a power supply issue.

In some instances, additional unusual symptoms may appear, such as a malfunctioning clock display on the instrument cluster or the inability to start the vehicle after a crash, as stored crash data can trigger an immobilizer‑like function.

Especially under thermal stress, the fault may occur sporadically—for example, the airbag system might function perfectly in cold temperatures, while the warning light illuminates when the cabin warms up.

In Which Vehicles Is the 8K0 959 655 K Control Unit Installed?

The airbag control unit with part number 8K0 959 655 K and its variants are mainly installed in vehicles based on Audi’s B8/8T platform. This includes, in particular, the Audi A4/S4 models of the B8 generation, as well as the Audi A5—both pre‑facelift and facelift versions.

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

Audi A4 / S4 (B8 / 8K type)

Audi A5 (8T type, model years 2007–2011)

Audi A5 Facelift (8T type, model years 2011–2016)

It is important to note that control units with functionally identical but different part numbers, such as 8K0 959 655 N, may also be installed in these vehicles. Our repair service covers these variants as well.

How does the control unit repair process work at Airbag24?

At Airbag24, every control unit undergoes a standardized repair process. This begins with an incoming inspection and reading of the fault memory. This is followed by professional component-level repair, erasure of stored crash data, and a final functional test to ensure full operability.

Before removal, it is ideal to have a diagnosis performed at a specialized workshop to confirm that the root cause of the fault lies in the control unit itself and not in peripheral components (e.g., sensors, wiring). Printing out the fault log is very helpful for our technicians during analysis.

Upon receipt at Airbag24, the control unit is subjected to a comprehensive examination. First, all stored faults and data are read out. Then, component-level repair takes place, replacing defective parts such as processors, memory chips, or capacitors and re-soldering connections.

A key step is the secure and complete erasure of stored crash data, thereby clearing the control unit for reuse. Following hardware repair, the unit is tested on a dedicated test bench to simulate proper system functionality and CAN-bus communication.

You receive 2 years' statutory liability for defects on every repair we perform.