B1303 airbag control unit fault

What does error code B1303 mean?

The B1303 error code in Mitsubishi vehicles indicates a specific issue with the “5bow sensor” within the Supplemental Restraint System (SRS). It means “Left = Off / Right = On,” signaling that the left 5bow sensor is inactive or faulty, while the right sensor is recognized as active. This fault compromises the proper monitoring of airbag components.

Technically, the 5bow sensor is a critical component for monitoring the airbag system’s status. When the airbag control unit receives an implausible status signal from this sensor—in this case, a discrepancy between the left and right sensors—the B1303 error code is set and stored in the fault memory.

The system then switches to a safety mode to prevent false activations. This is indicated to the driver by the continuously illuminated airbag warning light. The SRS’s primary function—responding correctly in the event of a crash—is compromised by this fault.

How do you recognize error B1303?

The main symptom of error B1303 is a permanently lit or flashing airbag warning light (SRS light) on the instrument panel. This warning remains active even after restarting the vehicle, alerting the driver to a malfunction in the restraint system that requires immediate inspection.

In the workshop, the fault is diagnosed by reading the fault memory using a suitable SRS diagnostic tool. The B1303 code appears there as an active or intermittent fault, providing crucial evidence of the issue with the 5bow sensor.

Other functional impairments, such as failures in other systems, are atypical for this error code. The fault is exclusively related to the integrity and functionality of the airbag system.

What causes B1303?

The most common cause of error code B1303 is a defect in the 5bow sensor itself or its associated peripherals. Issues like broken cables, corroded connectors, or damaged wiring disrupt communication with the airbag control unit. Less frequently, an internal fault may exist within the control unit itself.

A very common source of errors is physical damage to the wiring or sensors, which can result from mechanical impacts, material aging, or damage caused by animals such as martens. Defects in the seat occupancy mat can also be interconnected in some systems, leading to secondary faults that complicate diagnosis.

In certain cases, the fault is not due to external components but originates within the airbag control unit itself. For example, following a crash, the control unit may store internal crash data and become locked. Similarly, electronic components inside the unit can fail over time, triggering this error code.

Which vehicles are affected by B1303?

Error code B1303 occurs specifically in various models manufactured by Mitsubishi. Particularly affected are series such as the L200, Pajero Sport, Lancer, and Mirage. The exact cause may vary depending on the model and year of manufacture, but it always involves the airbag control unit and its sensor system.

At Airbag24, we repair error code B1303 for a range of specific Mitsubishi models, including the Mitsubishi Mirage CA, Mitsubishi Lancer CZ, Mitsubishi Lancer Evolution VI, the Mitsubishi Pajero Sport K90 (1996–2008), the Mitsubishi L200 of the K74 and KJ series (2015–2023), and the Mitsubishi Xpander Cross A05A.

How is error code B1303 professionally repaired?

Professional repair of error B1303 begins with a comprehensive diagnosis performed in the workshop. If the control unit is identified as the root cause, it is removed. After being sent to Airbag24, the device undergoes chip-level analysis, defective components are replaced, and a final functional test ensures quality.

The first step is always a systematic diagnosis of the vehicle. A specialized workshop should read the fault memory and inspect the peripherals—sensors, cables, and connectors—for physical damage. Often, the fault can already be resolved by replacing a defective sensor or repairing a cable harness.

If the defect is confirmed to lie within the control unit itself, it is removed and sent to a specialist like Airbag24. There, a detailed analysis of the circuit board and internal components is conducted. Defective parts are expertly repaired or replaced with new, high-quality components.

Following successful repair, the control unit undergoes a thorough functional test to ensure all system parameters once again meet the manufacturer’s specifications. The refurbished unit can typically be reinstalled in the vehicle without additional coding. We provide 2 years' statutory liability for defects on all repairs.