B0108 airbag control unit fault

What does error code B0108 mean?

Error code B0108 indicates a critical short circuit to battery positive (B+) in the passenger airbag ignition circuit. This means that a continuous, unwanted voltage supply is present, disrupting the activation circuit. The airbag control unit detects this electrical anomaly as a serious fault and, for safety reasons, deactivates the affected airbag circuit.

Technically speaking, the control unit continuously monitors the electrical parameters of the ignition circuits. A short circuit to B+ (battery positive) results in an implausible voltage reading outside the defined tolerances. The system can no longer reliably determine whether the airbag would deploy correctly in the event of a crash or if a false deployment might occur.

This fault is clearly a hardware issue within the wiring harness or connected components. The control unit’s role is to reliably detect such physical defects and report them by storing the error code and activating the warning light.

How do you recognize error code B0108?

The primary and unmistakable symptom of error code B0108 is the permanently illuminated airbag warning light on the instrument cluster. This light does not turn off after starting the vehicle, indicating an active, safety‑relevant fault in the restraint system. In some vehicles, a text message may also appear on the display.

The glowing warning light is a clear indication that the airbag system is not fully operational. In the event of a crash, the protective function of the passenger airbag—and potentially other components—cannot be guaranteed.

When diagnosed with a suitable workshop scanner, error code B0108 can be specifically retrieved from the airbag control unit’s fault memory. Attempting to erase the fault without addressing its physical cause usually fails, as the error is immediately detected again.

What causes B0108?

The main cause of error code B0108 is a physical short circuit in the passenger airbag circuit. Common triggers include damaged cables, corroded or loose connectors, and secondary damage from a previous accident. In some cases, crash data stored in the control unit following an airbag deployment can also trigger the fault.

Defective cables and connectors are the most frequent source of failure. Frayed insulation, kinked wires, or moisture inside a connector can cause the ignition circuit signal line to come into contact with a wire carrying constant voltage (Dauerplus).

Pre-existing damage from an accident is another typical cause. Even if the airbag did not deploy, impact forces can shift or damage cable bundles, leading to a short circuit at a later time.

After an airbag deployment, the control unit stores so‑called crash data and locks itself. Although the primary fault is a short circuit, such a control unit must also be cleared of these stored data to regain full functionality.

Which vehicles are affected by B0108?

Error code B0108 occurs in a range of vehicles from various manufacturers, particularly models from Toyota, Alfa Romeo, and Jaguar. Affected models include several generations of the Toyota Yaris and Corolla, the Alfa Romeo MiTo, and the Jaguar XE. Proper repair is essential for these models.

At Airbag24, we repair error code B0108 for a wide variety of control units. Frequently affected vehicles include:

Alfa Romeo: MiTo QV (955)

Jaguar: XE S (X760)

Toyota: Yaris (XP10, XP130, XP150, XP210), Yaris Cross, Yaris Hatchback, Corolla (E170, E210), Vellfire Hybrid, and IS (XP60).

How is error code B0108 professionally repaired?

Professional repair of error code B0108 begins with a thorough analysis of the submitted airbag control unit. First, the hardware is inspected for short circuits in the ignition circuit, and any stored crash data is erased if present. Next, the affected electronic components are repaired, followed by a final functional test.

At Airbag24, repairs follow a proven, professional procedure that ensures the complete functionality of the control unit.

Initially, the removed control unit undergoes a comprehensive incoming inspection in the lab. All relevant circuits are analyzed to pinpoint the exact source of the fault and confirm the short circuit.

In the next step, repairs are carried out at the component level. Technicians fix the short circuit in the ignition circuit and erase any crash data that may be blocking the control unit, thereby restoring its original functionality.

After repair, reprogramming the vehicle is not required, as the original configuration is preserved. A final check on the simulator ensures that error code B0108 has been permanently cleared and the control unit is functioning properly again.

This approach is a significantly more cost-effective alternative to purchasing a new control unit, which can cost several hundred euros. All repairs are covered by 2 years' statutory liability for defects.