Airbag control unit with part number 4M0 959 655 G

What is the function of the airbag control unit 4M0959655G?

The airbag control unit with part number 4M0959655G is the central control module of the passive safety system in the Bentley Bentayga Mk1 and Bentayga Speed. It continuously analyzes data from the acceleration sensors to trigger, within milliseconds, appropriate restraint systems such as airbags and seatbelt pretensioners in the event of a crash.

As a safety-critical component, it is precisely tailored to the vehicle architecture of the Bentley Bentayga. The module processes signals from various crash sensors distributed throughout the vehicle and, based on predefined algorithms, determines the type and severity of an impact.

Based on this analysis, the control unit 4M0959655G sends ignition commands to the corresponding pyrotechnic initiators of the airbags and seatbelt pretensioners. Therefore, its proper functioning is crucial for occupant protection.

Why does the control unit 4M0959655G fail?

The most common reason for a repair request is the storage of crash data after an accident. For safety reasons, the control unit then locks itself. Genuine defects are usually due to internal electronic hardware failures, such as memory chips, driver stages, or the internal power supply.

After an accident in which airbags or seatbelt pretensioners have deployed, irreversible crash data is stored in the control unit’s memory. This data cannot be erased using conventional workshop diagnostic tools and results in a permanently illuminated airbag warning light.

Furthermore, even without an accident, electronic components on the circuit board may fail. This often manifests as a complete loss of communication, where the control unit becomes unreachable via the diagnostic interface, or through specific internal fault codes.

How do you recognize a defect in the 4M0959655G?

The clearest symptom is the persistently illuminated airbag warning light on the instrument cluster. Additional signs include error messages such as “Airbag control unit defective” on the display, or the inability to read the control unit with a diagnostic tester—meaning no communication can be established.

The airbag warning light that fails to extinguish after starting the vehicle is the most common and obvious indication of a problem in the airbag system. This could point either to stored crash data or to an internal hardware failure within the 4M0959655G control unit.

Another typical symptom is the unavailability of the control unit. When the workshop attempts to read the fault memory, communication fails—the device does not respond to diagnostic requests, making precise fault analysis in the vehicle impossible.

In addition, specific fault codes may be stored in the fault memory, directly indicating an internal defect in the control unit or issues with sensors and actuators caused by the faulty control unit.

In which vehicles is the control unit 4M0959655G installed?

The part number 4M0959655G identifies a specific airbag module exclusively fitted in Bentley vehicles. It is explicitly designed for the first generation of the Bentayga and Bentayga Speed and is not compatible with other models or series.

At Airbag24, repairs for the control unit 4M0959655G are offered for the following models:

Bentley Bentayga 1st Generation (2016–2020)

Bentley Bentayga 1st Generation Facelift (2020–present)

Bentley Bentayga Speed Mk1

It is essential to verify the exact part number. Control units with different final letters or from other Bentley models, such as the Flying Spur Mk3, differ in both hardware and software and must not be used as replacements for safety reasons.

How is the 4M0959655G professionally repaired?

At Airbag24, each control unit undergoes a standardized process: Following an initial inspection and diagnosis, either the stored crash data is removed using specialized software, or defective electronic components on the circuit board are replaced. Final functional tests ensure quality, backed by 2 years' statutory liability for defects.

Upon submission to Airbag24, a visual inspection is first performed to detect mechanical damage or corrosion. This is followed by an electrical analysis, during which the fault memory is read to determine the exact cause of the issue—whether it is a crash entry or a hardware defect.

If stored crash data is present, it is erased from the control unit’s memory using specialized programming equipment, restoring the unit to its factory settings. If an electronic defect is detected, faulty components such as processors, memory chips, or voltage regulators are carefully desoldered and replaced under ESD‑safe conditions.

Subsequently, the control unit is thoroughly tested to ensure proper functionality. Following successful repair, the device is prepared for return shipment. Each repair comes with 2 years' statutory liability for defects.