B103604 airbag control unit fault

What does error code B103604 indicate in the airbag control unit?

Error code B103604 signifies a fault in the side‑airbag crash sensor on the passenger side. The airbag control unit detects an issue with the sensor or its peripheral components, suggesting either communication problems or a hardware defect that may impair the operation of the side‑airbag system.

Technically, the control unit reports that signal transmission from the side‑impact sensor on the passenger side is faulty. This sensor is critical for detecting a side impact and triggering the corresponding airbag in time.

An active B103604 error code causes the safety system to switch into a failsafe mode. In this state, proper activation of the passenger‑side airbag during a crash can no longer be guaranteed, posing a significant safety risk.

How do you recognize error code B103604?

The primary and unmistakable symptom of error code B103604 is the persistent illumination of the airbag warning light on the instrument panel. The fault remains stored in the diagnostic memory and can only be cleared after professional diagnosis and subsequent repair.

The warning light stays on even after restarting the engine, indicating a persistent, safety‑relevant fault in the system. Simply disconnecting the battery will not permanently erase the error from memory.

A specialized OBD2 diagnostic tool capable of reading the specific error codes of the airbag control unit is required for accurate diagnosis. Standard scanners may reach their limits in this case.

What causes B103604?

The most common causes of B103604 are physical defects in wiring or connectors. These include broken or shorted sensor cables, corrosion in connectors, loose contacts in the door‑junction connector at the A‑pillar, or mechanical damage to the sensor itself.

A typical source of trouble is the cable harness running through the door. Constant movement when opening and closing the door can lead to cable breaks or damaged insulation, disrupting signal transmission.

The door‑junction connector at the A‑pillar is particularly prone to corrosion caused by moisture ingress or mechanical wear. Defective or loose contacts in this area are a widespread cause of this error code.

The side‑impact sensor itself can also be damaged by water, humidity, or mechanical stress. In rarer cases, when all external components are intact, an internal defect in the airbag control unit’s circuit board—such as damaged circuits or faulty solder joints—may be responsible.

In which vehicles does B103604 occur?

Error code B103604 has been documented most frequently in Volkswagen vehicles. It particularly affects the VW e‑up! model series, including both the original version and the facelifted model throughout their entire production run.

At Airbag24, we professionally repair error code B103604 for the following specific models and series:

Volkswagen: e‑up! AA (model years 2013–2019) and e‑up! AA Facelift (model years 2019–2023).

The high incidence in these models is often attributed to the compact vehicle design and the resulting strain on door‑junction connectors and cable harnesses.

How is error code B103604 professionally repaired?

The repair follows a standardized process that begins with precise diagnostics. First, all external components—including cable harnesses, connectors, and the sensor itself—are inspected. If no issues are found here, the airbag control unit is examined for internal faults and repaired down to the component level.

At Airbag24, repairs begin with a thorough analysis upon receipt of the control unit. Before any work is performed on the airbag system, it is mandatory to disconnect the vehicle battery to prevent safety risks.

The diagnostic process includes a visual inspection of all relevant components, especially the door‑mounted cable harness and the door‑junction connector at the A‑pillar. Depending on the findings, defective cable harnesses and connectors are replaced according to manufacturer specifications, or corroded contacts are cleaned.

Next, the side‑impact sensor is checked and replaced if necessary. If the fault persists, this points to an internal defect within the control unit. In such cases, faulty electronic components on the circuit board are identified and professionally resoldered or replaced.

Upon completion of the repair, the error code is permanently erased from the diagnostic memory using an appropriate OBD2 diagnostic tool. 2 years’ statutory liability for defects is provided for the entire repair service.