Airbag control unit with part number 5Q0 959 655 BJ

What is the function of the Airbag Control Unit 5Q0 959 655 BJ?

The Airbag Control Unit 5Q0 959 655 BJ is the central control unit for the passive safety system in vehicles such as the Volkswagen Golf 7 and Audi A3 8V. It continuously monitors data from the vehicle’s sensors, processes this information, and within milliseconds sends ignition signals to the airbags and seatbelt pretensioners in the event of a crash.

As the brain of the restraint system, this control unit is responsible for reliably detecting a collision. It analyzes signals from acceleration and yaw rate sensors to determine the severity and type of impact.

Based on this analysis, the unit decides which restraint devices—such as front, side, or head airbags, as well as seatbelt pretensioners—should be deployed to provide optimal protection for occupants against serious injury. Repair offers an economically and technically sensible alternative to costly replacement.

What defects occur in the 5Q0 959 655 BJ?

Typical defects of the control unit 5Q0 959 655 BJ include stored crash data after an accident that cannot be erased, as well as internal software or communication errors. Errors in control unit coding or a complete loss of communication with the diagnostic tool also indicate a malfunction of the unit.

The most common reason for repair is the retention of crash data following a collision. Even after the vehicle has been repaired, the control unit remains internally locked, making reactivation impossible without professional reset procedures. In such cases, the airbag warning light stays illuminated.

Another area of failure involves internal software or communication malfunctions. These can cause the control unit to sporadically or permanently report faults, despite intact connected components like airbags and sensors.

In some instances, communication may fail entirely. The control unit becomes unreachable via the diagnostic interface (OBD), significantly complicating troubleshooting on the vehicle.

Defective or lost coding data can also trigger malfunctions. The control unit can no longer perform its specific functions correctly, leading to error messages and system failures.

How do you recognize a defect in the control unit 5Q0 959 655 BJ?

A defect in the control unit 5Q0 959 655 BJ primarily manifests as a continuously or intermittently illuminated airbag warning light in the instrument cluster. Additional symptoms include loss of communication with the diagnostic tool and failure when attempting to clear stored fault or crash data.

The clearest indication is the red airbag warning light. If it remains lit after starting the engine, the system signals a critical fault. It is vital to understand that with an active warning light, the entire airbag system is disabled and will not deploy in the event of a crash.

During workshop diagnostics, a defect often becomes apparent when the control unit cannot be accessed. Attempts to read the fault memory fail because no connection can be established with the control unit.

An active fault in the airbag system inevitably results in failure during the main inspection (HU). Using simulators or jumpers is not only life‑threatening but also leads to immediate revocation of the vehicle’s operating permit.

In which vehicles is the control unit 5Q0 959 655 BJ installed?

The airbag control unit with part number 5Q0 959 655 BJ is mainly found in models from the Volkswagen Group. This includes the Volkswagen Golf 7 of the AU series, as well as the Audi A3 of the 8V series, particularly the Sportback and its corresponding facelift model.

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

Volkswagen: Golf 7 (AU series)

Audi: A3 (8VS Sportback series, 2012–2016) and A3 (8VS Sportback facelift series, 2016–2020)

How does the repair of the control unit 5Q0 959 655 BJ proceed?

Repair of the control unit 5Q0 959 655 BJ at Airbag24 begins with reading the fault memory in the vehicle. After removal and shipment of the unopened unit, technicians analyze it. Using specialized software, crash data is cleared and internal faults are corrected. Each repair undergoes a final inspection and is backed by 2 years’ statutory liability for defects.

For targeted repair, it is advisable to read the fault memory before removing the control unit and to attach the shipping record. The device must be sent for repair unopened, as improper opening attempts could damage the electronics.

Upon receipt at Airbag24, specialized technicians perform a thorough analysis. The primary focus is on eliminating the root cause of the fault, such as professionally resetting stored crash data or correcting software errors at the chip level.

Following successful repair, the control unit is thoroughly tested. In some vehicles, after reinstallation, the vehicle’s fault memory must be cleared again. We provide 2 years' statutory liability for defects on all repairs performed.