B1155 airbag control unit fault

What does error code B1155 mean in the airbag control unit?

Error code B1155 indicates a critical fault in the power supply of the airbag control unit (SRS module). This error is typically triggered by a sudden voltage drop, an interruption in the power supply, or unstable voltage levels—conditions that can occur during a jump start or battery replacement. The control unit registers this as a permanent hardware fault and illuminates the airbag warning light.

Technically speaking, the SRS module continuously monitors its own supply voltage. If this voltage deviates from the predefined set points—even for a brief moment—the B1155 error is logged in the internal fault memory. This entry is often marked as non‑erasable, as the system assumes a potentially safety‑critical defect that could compromise the proper functioning of the airbags in an emergency.

The result is that the airbag system enters a safety mode, with the airbag warning light remaining steadily illuminated to alert the driver. Simply clearing the fault memory using a standard diagnostic tool usually proves unsuccessful.

How do you recognize error B1155?

The primary symptom of error B1155 is a permanently lit airbag warning light (SRS indicator) on the instrument cluster. Often, communication with the airbag control unit via a diagnostic tool cannot be established. Even if a connection is possible, error code B1155 cannot be cleared from the fault memory and reappears immediately.

The most obvious sign is the airbag warning light that fails to turn off after starting the vehicle, indicating that the safety system is not fully operational and the airbags may not deploy in the event of a crash.

Another typical characteristic is that workshops equipped with professional diagnostic systems such as Autocom or Delphi can read the fault memory, yet error code B1155 remains a static, permanent fault. Any attempt to clear it fails, pointing to a deeper defect within the control unit itself.

What causes error code B1155?

The primary cause of B1155 is an unstable or interrupted power supply, often resulting from external events like a jump start, battery replacement, or a deeply discharged battery. Additional causes include physical defects such as loose or corroded cable connections to the control unit, or an internal short circuit on the circuit board.

Voltage drops or spikes are the most common source of errors. The sensitive SRS module reacts to such anomalies by entering a permanent fault state to prevent malfunction during a crash.

Even a brief interruption of power while the ignition is on can be enough to trigger the error code—for example, when working on the vehicle’s electrical system.

Finally, hardware defects in the control unit itself or its peripherals may also be responsible. These include corrosion at connector contacts due to moisture ingress or damaged cables leading to intermittent connections.

In which vehicles does error B1155 frequently occur?

Error code B1155 is particularly common in certain models from Nissan and Seat. Specifically, various generations of the Nissan Qashqai and the Seat Leon are disproportionately affected by this particular power‑supply issue in the airbag control unit.

At Airbag24, we repair error code B1155 for the following models, where this defect occurs most often:

Nissan: Qashqai J10 (2006–2010) and J10 Facelift (2010–2013)

Nissan: Qashqai J11 (2013–2017) and J11 Facelift (2017–2021)

Nissan: Qashqai J12 (2021–2024)

Seat: Leon Xcellence Mk3

How is error B1155 professionally repaired?

Professional repair of error B1155 requires component‑level analysis. After receiving the removed control unit, the circuit board is inspected for damage, defective components such as voltage regulators or capacitors are replaced, and the software is then reset to erase the permanent fault and any associated crash data.

At Airbag24, repairs follow a proven, multi‑step process. First, upon arrival, the control unit is opened and subjected to a thorough visual inspection. Technicians specifically look for corrosion, burn marks, or other visible damage to components and traces.

In the next step, relevant electronic components—especially those related to the power supply—are tested and replaced as needed. Defective voltage regulators, capacitors, or fuses are carefully desoldered and replaced with new, high‑quality parts.

Finally, a connection is established to the control unit’s processor using specialized hardware and software. The internal fault memory is completely reset (reset), thereby removing the permanently flagged error B1155. Any stored crash data is also erased during this process.

Following successful repair, the control unit is fully functional again and can be installed in the vehicle via plug-and-play. We provide 2 years' statutory liability for defects on the completed repair.