Airbag control unit with part number A 171 820 43 26

What is the function of the airbag control unit A 171 820 43 26?

The airbag control unit A 171 820 43 26 from Temic is the central safety module for the Mercedes-Benz SLK-Class R171. It processes data from crash sensors in real time to deploy life-saving components—such as driver, passenger, side, and curtain airbags—in milliseconds during a collision, while also storing relevant crash data.

As the brain of the passive safety system, this component continuously monitors signals from acceleration sensors and other critical vehicle sensors. In the event of a collision, it evaluates incoming data to determine whether and when to deploy the airbags, ensuring optimal protection for occupants.

Additionally, the unit communicates with the vehicle’s on-board diagnostics (OBD) system and logs system-relevant fault codes. A malfunctioning control unit not only poses a significant safety risk but may also result in the loss of the vehicle’s operating permit.

What types of defects occur in A 171 820 43 26?

Typical defects of the A 171 820 43 26 control unit include internal electronic failures that often occur independently of any accident. Common causes are faulty components on the circuit board, which can trigger error code 900E, or a loss of communication with the diagnostic tool. Stored crash data that cannot be erased is another frequent issue.

A commonly diagnosed problem is an internal electronic failure, often logged in the fault memory under code 900E. This indicates hardware damage on the circuit board—such as processors, capacitors, or other electronic parts—and is particularly prevalent in the SLK R171.

Another issue is complete communication failure. In such cases, the control unit becomes unresponsive via the diagnostic interface, making fault analysis impossible and keeping the airbag warning light permanently illuminated.

Following a collision, crash data is stored within the unit, preventing the system from being reactivated. If this stored data cannot be cleared, hardware repair is required. Errors related to the vehicle identification number may also point to a defect in the internal memory.

The repair procedures for this control unit are often identical across similar part numbers, such as A1718202426, A1718203126, A1718203626, and A1718204126, as these units share very similar technical designs.

How do you recognize a defect in the airbag control unit?

A defect in the A 171 820 43 26 control unit primarily manifests as a permanently lit or flashing airbag warning light on the instrument cluster. Additional signs include the inability to communicate with a diagnostic tool or the failure to clear stored fault codes—such as the internal error code 900E—even when no crash has occurred.

The most obvious symptom is the persistently illuminated airbag indicator light. It signals a fault in the restraint system and does not extinguish after starting the vehicle, unlike a functioning system.

A workshop diagnostic tool cannot establish a connection with the airbag control unit. The module fails to respond to queries, hindering precise fault diagnosis and suggesting a serious internal defect.

Stored fault codes remain unerasable. Even after addressing external causes—such as replacing a seat occupancy mat—the error code persists in the control unit, keeping the warning light active.

In some cases, drivers report specific issues, such as problems with side sensors or the driver’s airbag, despite having already replaced related components like the coil spring. This suggests the root cause lies within the control unit itself.

An important safety note: Using airbag simulators, resistors, or other bypass devices to disable the warning light is illegal and extremely dangerous. Work on the airbag system must be performed exclusively by qualified professional workshops.

In which vehicles is A 171 820 43 26 installed?

The airbag control unit A 171 820 43 26 and its variants are specifically designed for the Mercedes-Benz SLK-Class R171 series. It serves as the central safety component across all engine options and trim levels of the SLK R171 convertible, produced from 2004 to 2011. Airbag24 offers repairs tailored to this exact model range.

At Airbag24, we repair the A 171 820 43 26 control unit for the following model:

Mercedes-Benz SLK-Class R171 Convertible (2004–2011)

How does repair work at Airbag24?

After sending the removed A 171 820 43 26 control unit to Airbag24, professional repair of the internal electronics takes place. Technicians replace defective components such as processors or capacitors. Following a successful functional test, the unit is returned, backed by 2 years' statutory liability for defects on the repair. With this control unit, erasing the crash data is often not possible. If the crash data needs to be erased, please contact us briefly before sending the unit in – we will check your part number.

As a first step, before removing the control unit, please read out the fault memory and include the transmission log. Depending on the model variant, the unit is located either under the center console or beneath the passenger seat.

Upon receipt at Airbag24, our technicians perform a detailed analysis of the circuit board. Defective electronic components are identified and replaced with high-quality new parts.

Subsequently, the repaired control unit undergoes a comprehensive functional test to ensure proper operation of all system components. Only after passing this test is it approved for return shipment.

After reinstalling the unit in your vehicle, you may need to clear the vehicle’s fault memory once. We provide 2 years' statutory liability for defects on every repair performed.