Airbag control unit with part number 4M0 959 655J

What is the function of the airbag control unit 4M0 959 655J?

The airbag control unit 4M0 959 655J is the central control module for the entire passive safety system (Supplemental Restraint System, SRS) in the Volkswagen Touareg CR from model year 2018 onwards. It processes data from crash sensors and determines whether and which airbags or seatbelt pretensioners need to be deployed in the event of a collision.

As the “brain” of the restraint system, this control unit is specifically designed for the vehicle architecture of the third-generation VW Touareg (Type CR). It is typically installed in the center console area, where it ensures communication with all relevant safety components. Its primary task is to continuously monitor system readiness and, in the event of an impact, activate the appropriate protective measures within milliseconds.

The proper functioning of this control unit is critical for survival, as it coordinates the deployment of front, side, and head airbags, as well as pyrotechnic seatbelt pretensioners, to provide optimal occupant protection.

Why does the airbag control unit 4M0 959 655J fail?

The most common cause of failure for the 4M0 959 655J control unit is the permanent storage of crash data after an accident. Other defects arise from electrical issues such as damaged wiring and connectors, or from internal electronic faults on the circuit board that result in specific diagnostic trouble codes.

Following an airbag deployment, the unit permanently stores crash data. This lock cannot be cleared using standard diagnostic equipment, making professional repair or replacement essential. After an accident, the device effectively enters a safety‑locked state.

Electrical problems are another frequent source of failure. These include broken or damaged wires leading to SRS components, such as the side airbags. Loose or corroded connectors can also disrupt communication and lead to malfunctions. In some cases, a fault may be triggered by adjusting the seat position, indicating a defective cable connected to the seatbelt pretensioner.

In addition, internal hardware defects on the circuit board may occur. Error codes such as “side sensor error” or “internal airbag error” often point to such a defect, requiring component‑level repair.

How do you recognize a fault in the 4M0 959 655J control unit?

A fault in the airbag control unit 4M0 959 655J usually manifests as a constantly illuminated airbag warning light on the instrument cluster. Additional symptoms include specific diagnostic trouble codes stored in the fault memory or complete inability to communicate with the control unit during an OBD2 diagnostic session.

The primary indicator is the activated SRS or airbag warning light. This signals a malfunction in the safety system and fails to extinguish after starting the vehicle, indicating a problem that requires immediate inspection.

Using a suitable workshop diagnostic tool, specific error codes can be retrieved. Entries such as “side sensor error” or “internal airbag error” provide direct clues about the nature of the issue and help narrow down its cause.

In severe cases, the control unit may completely lose communication with the diagnostic tool. This total loss of connectivity suggests a more serious internal hardware failure.

In which vehicles is the 4M0 959 655J control unit installed?

The airbag control unit with part number 4M0 959 655J is specifically designed for the third generation of the Volkswagen Touareg. At Airbag24, we professionally repair this control unit for the model series listed below, restoring full functionality to the safety system.

At Airbag24, we repair the 4M0 959 655J for the following model:

Volkswagen Touareg CR (from model year 2018 onward)

How does the repair of the 4M0 959 655J control unit work?

The repair process at Airbag24 includes precise fault diagnosis, professional removal, shipment of the unit, and expert refurbishment. During this process, crash data is erased, and defective electronic components are replaced. Following a successful functional test, your unit is returned with 2 years' statutory liability for defects.

Before removing the control unit from the center console, it is recommended to read out the fault memory to document all relevant diagnostic trouble codes. The unit is then carefully packaged and sent to Airbag24.

Upon receipt at Airbag24, our technicians conduct a thorough analysis. The repair focuses on addressing the root cause—whether erasing crash data, repairing circuit board damage, or replacing faulty sensors and memory modules. Finally, the control unit undergoes testing on a bench to ensure full functionality.

The repaired unit will be shipped back to you. After reinstallation, a final diagnostic is recommended to ensure the entire SRS system is functioning properly. It is also essential to inspect all other SRS components, such as airbags and seatbelt pretensioners, and replace them if necessary.