Airbag control unit with part number A117 900 58 00

What is the function of the airbag control unit A117 900 58 00?

The airbag control unit with Mercedes-Benz part number A117 900 58 00 is the central control module of the occupant safety system (SRS) in certain CLA models. It processes data from crash and acceleration sensors to precisely and millisecond‑fast deploy the life‑saving airbags and seatbelt pretensioners in the event of a collision. It is directly responsible for the safety of vehicle occupants.

As the heart of the safety system, this control unit continuously monitors all connected components, including the various airbags (driver, passenger, knee), the seatbelt pretensioners, as well as their associated sensors and ignition circuits. It ensures that the system remains operational at all times and communicates any malfunctions to the driver via the SRS warning light on the instrument cluster.

Technically, this module is closely networked with other control units in the vehicle. In industry circles and repair databases, part number A117 900 58 00 is often referenced alongside Bosch number 0 285 011 863 and replacement numbers 1179005800 and 1179008600, which can be used in the same vehicle platforms.

Why does the A117 900 58 00 control unit fail?

The most common cause of failure or malfunction of the A117 900 58 00 control unit is the storage of crash data after an accident. The system locks the unit to prevent reuse without proper inspection. Other causes include internal electronic defects in components such as memory chips, driver stages, or the power supply.

Following an accident—even minor collisions where seatbelt pretensioners or airbags were deployed—the control unit permanently records the crash event in its internal memory. This lockout is a manufacturer‑imposed safety feature, resulting in a constantly illuminated airbag warning light. The system remains inactive until the crash data is professionally cleared and the unit is reset.

In addition to crash data, purely electronic faults may also occur. Cold solder joints caused by thermal stress and vibration over years, or the failure of individual components like capacitors, resistors, or ICs on the circuit board, can lead to communication issues or complete system failure. Moisture ingress into the housing can also cause irreparable corrosion, although targeted component repairs are often possible.

How do you recognize a defect in the A117 900 58 00 airbag control unit?

The clearest symptom is the persistently illuminated airbag or SRS warning light on the dashboard. Another clear indication is when the control unit cannot be read by a diagnostic tool (no communication). Often, fault codes related to activated components remain stored even after those parts have been replaced.

A primary sign is the airbag warning light that stays on continuously. It does not turn off after starting the vehicle, indicating a serious, safety‑critical error within the SRS system detected by the control unit.

It frequently happens that workshops lose access to the control unit. When attempting to read the fault memory via the OBD interface, the diagnostic tool reports a communication error. The control unit no longer responds, pointing to an internal electronic fault.

Especially after accident repairs, a typical pattern emerges: despite the professional replacement of all deployed airbags and seatbelt pretensioners, the corresponding fault codes in memory cannot be erased. Error messages such as “Crash data stored,” “Driver airbag deployed,” or “Crash sensor defective” persist indefinitely because the control unit remains internally locked.

In which vehicles is the A117 900 58 00 control unit installed?

The A117 900 58 00 airbag control unit is specifically designed for Mercedes‑Benz CLA‑class models. At Airbag24, we repair this control unit for the Mercedes‑Benz CLA-Class X117 Shooting Brake and the subsequent CLA X118 Shooting Brake. Repair offers a cost‑effective alternative to expensive new purchases.

At Airbag24, we specialize in repairing this specific control unit for the following models:

Mercedes‑Benz:

CLA X117 Shooting Brake (model years approx. 2015–2019)

CLA X118 Shooting Brake (model years from 2019 onward)

How is the A117 900 58 00 control unit repaired?

Repair at Airbag24 follows a standardized process. Upon receipt, the control unit undergoes an initial inspection to read fault memories and crash data. This is followed by component‑level repair, clearing of crash data, and a final functional test on a specialized test bench. You receive 2 years' statutory liability for defects on the repair.

Once the removed control unit has arrived at Airbag24, it undergoes a professional and transparent repair process:

1. Initial Diagnosis: First, a visual inspection is performed for external damage. Then, the unit is connected to specialized test equipment to fully read out the internal fault memory and any stored crash data.

2. Electronic Analysis: Our technicians open the device and analyze the circuit board at the component level. This includes checking the power supply, memory chips, processors, and the driver stages for the ignition circuits of the airbags and seatbelt pretensioners.

3. Repair: Defective electronic components are identified and replaced with new, high-quality parts. If necessary, stored crash data is erased from the control unit’s memory to remove any immobilization locks.

4. Final Test: After repair, the control unit is connected to a test bench that simulates a complete vehicle. All functions—from communication to activation of individual safety components—are thoroughly tested. The unit leaves our facility only when it operates flawlessly.

Following return shipping and reinstallation, you simply need to clear the fault memory in the vehicle. The airbag warning light should then turn off.