Airbag control unit with part number 4B0 959 655 E

What is the function of the airbag control unit 4B0959655E?

The airbag control unit with part number 4B0959655E is the central control module for the passive safety system in vehicles such as the Audi A6 C5 and RS6 C5. It continuously processes data from acceleration and yaw rate sensors to deploy airbags and seatbelt pretensioners within milliseconds in the event of a crash.

This unit is critical for occupant protection. It constantly monitors all components connected to the restraint system, from front and side crash sensors to individual airbag modules and seatbelt pretensioners. Any irregularity is immediately reported to the instrument cluster, activating the airbag warning light.

In addition, the control unit communicates with other vehicle systems to perform functions such as cutting off fuel supply or unlocking doors in an emergency. Therefore, proper operation is essential for overall vehicle safety.

Why does the airbag control unit 4B0959655E fail?

The most common causes of failure for the 4B0959655E control unit are internal electronic malfunctions, stored crash data after an accident, or secondary damage caused by moisture. Improper repair attempts in the past can also result in irreparable damage, increasing the complexity of restoration.

A primary defect involves hardware issues. Electronic components on the circuit board, such as sensors or memory chips, may fail due to age or external factors. This often leads to complete system failure or persistent error messages that cannot be cleared.

After a crash, the unit stores so‑called crash data—a safety feature that prevents reuse without professional diagnostics. The control unit becomes locked and must be professionally reset to restore functionality.

This control unit is also known under replacement and equivalent part numbers 4B0959655TB, 4B0959655C, 4B0959655G, 4B0959655AA, 4B0959655J, or 4B0959655M, which often exhibit similar fault patterns.

How do you recognize a defect in the 4B0959655E control unit?

A defect in the 4B0959655E control unit typically manifests as a permanently illuminated airbag warning light on the instrument cluster. Another clear indication is the lack of communication with diagnostic equipment, making it impossible to read the fault memory via the OBD interface.

The most noticeable symptom is the airbag warning light, which fails to turn off after engine start-up or flashes sporadically during driving. This signals a critical fault in the restraint system that requires immediate inspection.

When workshops attempt to read the fault memory, they often receive no response from the control unit. It becomes unreachable to the diagnostic system, complicating accurate fault analysis and pointing directly to an internal module malfunction.

Additionally, secondary faults may occur, such as implausible readings from wheel speed sensors—even after they have been replaced—or a failure of the speedometer display. However, before removal, a professional diagnosis should always confirm that the control unit is indeed the source of the problem.

In which vehicles is the 4B0959655E control unit installed?

The airbag control unit with part number 4B0959655E is specifically used in various models of the Audi A6 and RS6 C5 series. Repairs cover both sedan and Avant variants, as well as different production periods within this generation.

At Airbag24, we repair part number 4B0959655E and its variants for the following Audi models:

Audi A6 C5 (Type 4B, model years 1997–2001) Audi A6 C5 Facelift (Type 4B, model years 2001–2005) Audi RS6 C5 (model years 2002–2004) Audi S6 C5 (Type 4B, model years 1999–2005)

How is the 4B0959655E control unit professionally repaired?

Professional repair at Airbag24 restores full functionality to the control unit. The process includes component-level diagnostics, replacement of defective parts, secure deletion of crash data, and a final functional test. Each repair comes with 2 years' statutory liability for defects.

Once the removed control unit arrives at Airbag24, technicians conduct a detailed incoming inspection. They analyze the electronics to pinpoint the exact cause of the fault. Defective components on the circuit board are identified and replaced with new, high-quality parts.

A key step is resetting the internal memory. Stored crash data is completely and securely erased, ensuring the control unit is fully operational again. Subsequently, the unit is tested on a specialized test bench to simulate and verify the correct functioning of all systems.

Repair is a cost-effective and sustainable alternative to expensive new purchases. The refurbished control unit functions just like a brand-new part and can be reinstalled in your vehicle without additional programming or coding (plug-and-play).