B120E airbag control unit fault

What does error code B120E mean in the airbag control unit?

Error code B120E indicates a specific hardware or wiring fault in the airbag system. The error description reads “High resistance in the driver airbag igniter.” This means the control unit is detecting an abnormal electrical value in the driver airbag’s ignition circuit, which prevents the airbag from deploying in an emergency and results in deactivation of the system.

Technically speaking, the airbag control unit (SRS module) continuously monitors the electrical characteristics of all connected components. The driver airbag’s ignition circuit must maintain a precisely defined resistance level for the system to be considered operational.

When error B120E occurs, this resistance threshold has been exceeded. The control unit interprets this as an open circuit or a defect in the electrical path. To prevent unintended deployment, the airbag warning light illuminates, and the affected airbag is deactivated.

How can you recognize error B120E?

The primary and unmistakable symptom of error code B120E is the persistent illumination of the red airbag warning light on the instrument cluster. It does not extinguish after starting the vehicle. This is a clear indication that the occupant protection system is not fully functional and requires immediate inspection.

In many vehicles, especially Audis, an additional message may appear in the Driver Information System (FIS), alerting you to a malfunction in the airbag or restraint system.

Using a suitable workshop diagnostic tool, error B120E can be clearly retrieved from the airbag control unit’s fault memory. Other symptoms, such as communication issues, are atypical for this particular error code.

What causes error B120E?

The main cause of error B120E is excessively high electrical resistance in the driver airbag’s ignition circuit. This can result from a defective airbag igniter, damaged wiring, corroded connectors, or—very commonly—a built-in hardware failure within the airbag control unit itself, such as a faulty output stage.

A frequent culprit is an internal defect on the airbag control unit’s circuit board. In particular, the output stage that drives the driver airbag’s ignition circuit may fail due to aging or prior electronic damage, directly triggering error B120E.

Peripheral issues are also possible. Damaged cables or a defective coil spring in the steering wheel can disrupt the electrical circuit. Similarly, corroded or loose connectors between the control unit and the airbag can raise resistance beyond acceptable limits.

Rarely, the fault lies directly in the pyrotechnic igniter of the airbag assembly. A systematic workshop diagnosis is required to pinpoint the exact source of the problem among the control unit, wiring, and airbag.

In which vehicles does error B120E occur?

Error code B120E is a well-known, model-specific issue that primarily affects Audi vehicles. Especially the sporty S5 models have been impacted across multiple production years. At Airbag24, we specialize in repairing precisely these control units.

At Airbag24, we repair error code B120E for the following models:

• Audi S5 F5 (model years 2016–2019)

• Audi S5 F5 Facelift (model years 2019–2024)

The prevalence of this error in these models points to a typical weakness in the hardware used in these control units, which can be reliably resolved through professional repair.

How is error B120E professionally repaired?

A professional repair of error B120E focuses on the electronic restoration of the airbag control unit. Upon receipt, the device is thoroughly analyzed; defective components on the circuit board, such as resistors or transistors, are replaced, and the fault memory is cleared. Final tests ensure full functionality.

At Airbag24, repairs follow a standardized process. After receiving the removed control unit, a detailed diagnosis is performed to confirm error B120E and rule out any additional damage, such as moisture-related issues.

The critical step is component-level repair. Our technicians locate the faulty parts on the main circuit board responsible for the abnormal resistance reading and replace them with precision. This approach is not only more cost-effective than replacing the entire unit but also more sustainable.

Following hardware restoration, all fault codes and any crash data stored in the control unit are erased. The device is returned to its factory settings. A final functional test on a test bench simulates real‑world operation in the vehicle, ensuring that all ignition circuits function flawlessly.

The repaired control unit is ready for immediate use after installation (Plug & Play). We provide 2 years' statutory liability for defects on every repair.