B1302 airbag control unit fault

What does error code B1302 mean?

Error code B1302 indicates a fault in the coil circuit of the accessory delay relay within the airbag control unit. This relay controls safety‑related functions. In specific Mitsubishi models, the code points to a fault with the left 5‑bow sensor, which is reported as active while the right sensor remains inactive.

Technically, the control unit monitors resistance and voltage in the coil circuit of the accessory delay relay. If the measured values deviate from the target values stored in the control unit, error code B1302 is logged. The relay is responsible for the timed power supply to airbag system components.

In the affected Mitsubishi models, the fault is interpreted more specifically as “5bow sensor L ON / R OFF,” meaning that the left sensor (part of the advanced airbag sensor system) sends a signal, while no signal is received from the right sensor. This inconsistency triggers the control unit to switch into safety mode and activates the airbag warning light.

How do you recognize error code B1302?

The primary and unmistakable symptom of error code B1302 is the permanently illuminated airbag warning light on the instrument panel, which does not turn off after starting the vehicle. Reading the fault memory with an appropriate diagnostic tool confirms the specific B1302 code in the airbag system.

The activated airbag warning light is a clear indication that the entire safety system (SRS – Supplemental Restraint System) may be malfunctioning. In the event of a crash, airbag deployment and seatbelt pretensioners could be impaired or completely disabled.

Other direct symptoms that the driver might notice are generally absent. The functionality of other vehicle systems remains unaffected. The only reliable diagnosis comes from reading the fault memory of the airbag control unit.

Why does B1302 occur?

The main cause of error code B1302 is an electronic fault on the airbag control unit’s circuit board, specifically in the circuit of the accessory delay relay. This can result from defective components or faulty solder joints. In Mitsubishi models, the root cause often lies in the 5‑bow sensor system or its control circuitry.

The defect manifests at the component level—typically in the circuits driving the relay coil or in the relay itself. Aging of electronic components, thermal stress, or vibrations can lead to such failures over time.

Before confirming the control unit as the source of the problem, external causes should be ruled out. This includes checking connectors on the control unit and sensors, especially under the seats. Mechanical components like seatbelt locks can also trigger error messages, even though B1302 strongly suggests an internal fault.

Which models experience B1302?

Error code B1302 is particularly common in various Mitsubishi models, including specific series such as the Mirage, Lancer, Lancer Evolution, Pajero Sport, L200, and Xpander Cross. Repairing this issue is a proven and cost‑effective solution for these vehicles.

At Airbag24, error code B1302 is professionally repaired for a range of Mitsubishi vehicles. Our expertise covers the following specific models and series:

Mitsubishi Mirage CA

Mitsubishi Lancer CZ

Mitsubishi Lancer Evolution VI

Mitsubishi Pajero Sport K90 (model years 1996–2008)

Mitsubishi L200 K74

Mitsubishi L200 KJ (model years 2015–2023)

Mitsubishi Xpander Cross A05A

How is B1302 professionally repaired?

Professional repair of error code B1302 focuses on refurbishing the removed airbag control unit. Following an initial inspection, defective electronic components on the circuit board—especially in the area of the accessory delay relay and sensor control—are identified and replaced. Finally, the unit is tested, and the fault memory is cleared.

The process at Airbag24 is designed for maximum safety and efficiency. After removal, the control unit is sent for analysis. First, error code B1302 is verified in the lab to reliably rule out external causes.

The actual repair takes place at the circuit board level. Technicians inspect and replace faulty components in the relay coil circuit. Connectors and terminals are cleaned and checked. For Mitsubishi models, special attention is paid to calibrating and synchronizing the 5‑bow sensor system.

Following successful repair, a software reset is performed and all fault codes are cleared. A final functional test on a test bench simulates vehicle conditions and ensures the control unit is functioning properly again. A 12-month warranty is provided for the completed repair.