C1605 airbag control unit fault

What does error code C1605 mean?

Error code C1605 indicates an internal fault in the airbag control unit. Often, the error description reads “Test not completed,” suggesting a problem with the internal electronics or the diagnostic process. For certain manufacturers such as Renault or Dacia, this code may also appear in conjunction with issues related to the electric power steering system.

Technically speaking, this means that the control unit’s self-diagnosis fails during system startup. Internal components like microcontrollers or memory chips cannot successfully complete the required tests, causing the entire airbag system to be deactivated as a precautionary measure.

The control unit is unable to report its status correctly to the vehicle’s electrical system, resulting in the airbag warning light remaining constantly illuminated. This is a safety-critical fault that prevents the airbags from deploying in the event of a crash.

How can you recognize error C1605?

The primary and unmistakable symptom of error C1605 is the permanently lit airbag warning light on the instrument panel. Additionally, in models where this fault is linked to the power steering system, you may experience a failure or impairment of steering assistance.

The airbag warning light does not turn off after starting the vehicle, indicating that the safety system is not operational. The vehicle would fail a mandatory technical inspection if this active fault were present.

Another sign is that while the fault memory can be read using a diagnostic tool, error code C1605 cannot be permanently cleared. It reappears immediately because the underlying hardware issue persists.

What causes error C1605?

The main cause of error code C1605 is an internal electronic fault within the airbag control unit itself. Other common triggers include damaged connectors, malfunctions in the steering angle sensor, or a defective slip ring—especially in Renault and Dacia vehicles, where this error code has been documented.

An internal defect may result from faulty electronic components such as capacitors, microcontrollers, or damaged circuit traces. Aging, moisture, or short circuits can exacerbate these damages.

Mechanical stress, for example from frequent seat adjustments beneath the seat, can loosen or damage the connectors on the airbag control unit, leading to loose connections or signal interruptions.

In certain Renault models, this code is closely associated with the electric power steering system. A malfunction in the steering angle sensor or the slip ring (also known as a brush ring), which transmits signals from the steering wheel, can likewise trigger error C1605.

In which vehicles does error C1605 occur?

Error code C1605 has been specifically documented for certain models of Renault and Dacia. Airbag24 offers professional, cost-effective repairs for the affected airbag control units of these vehicles, restoring full functionality to the safety system.

At Airbag24, error code C1605 is repaired for the following models and series:

Dacia: 1300 I

Renault: Captur I (2013–2019), 18 I (1978–1994)

How is error C1605 repaired?

Professional repair of error C1605 focuses on restoring the control unit’s electronics. After sending the removed airbag control unit to Airbag24, a detailed analysis is performed, defective components are replaced, any stored crash data is erased, and a final functional test ensures quality.

The process begins with the proper removal of the airbag control unit from the vehicle and its secure shipment to the specialized laboratory. Before dismantling, the vehicle battery must be disconnected without fail.

At Airbag24, a systematic fault analysis is first conducted to pinpoint the exact cause of error C1605 on the circuit board. This may involve identifying short circuits or defective components.

Subsequently, defective electronic parts such as capacitors, microcontrollers, or fuses are replaced with high-quality new components. If crash data remains stored in memory following an accident, it is completely erased, as it can lead to persistent error messages.

Following repair, the control unit undergoes comprehensive testing to confirm proper operation. Two years' statutory liability for defects is provided for all repairs performed.