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B179A

DTC B179A indicates the SRS (Supplemental Restraint System) ECU detects an open circuit or disconnected front passenger-side second-stage seat belt pretensioner — Atto 3

Safety System

DTC B179A indicates the SRS (Supplemental Restraint System) ECU detects an open circuit or disconnected front passenger-side second-stage seat belt pretensioner.

The "second stage" typically refers to the retractor pretensioner (distinct from the first-stage buckle pretensioner), which uses a pyrotechnic igniter to rapidly tighten the seat belt during a collision.

The SRS ECU monitors the pretensioner circuit resistance (normally 2.0-4.0 Ω) to determine connection status.

The ECU sets this DTC when resistance exceeds the threshold (typically >10 kΩ or a complete open circuit).

This fault prevents pretensioner activation during a collision, reducing chest and head restraint protection for the front passenger, and illuminates the instrument panel airbag warning light.

Because occupants of various body sizes frequently adjust the front passenger seat, this fault occurs significantly more often in shared vehicles than on the driver side.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Frequent seat adjustment loosened the connector

✓
A 2021 BYD Tang DM with 32,000 km presented with an intermittently illuminated airbag warning light. A VDS scan returned DTC B179A-00 (current fault). Inspection revealed the front passenger seat pretensioner connector lock tab had fractured beneath the seat; frequent adjustment by different occupants had caused the connector to work loose. Replaced the connector with an OEM unit, rerouted the wiring harness, and secured it with cable ties to prevent movement with the seat. Fault permanently resolved.
BYD DTC AI Analysis

Connector oxidised and corroded after water ingress

✓
2019 BYD Yuan EV. Airbag warning light stayed on after wading through approximately 30 cm of water. Scan tool showed B179A. Removed the passenger-side B-pillar trim and found water staining and green copper corrosion inside the pretensioner connector. Terminal oxidation caused contact resistance exceeding 50 Ω. Cleaned the terminals with precision electronic cleaner, applied conductive protective grease, and replaced the waterproof seal ring. Advised the owner to inspect the door seals and avoid driving through water.
BYD DTC AI Analysis

Open circuit in pretensioner gas generator

✓
2020 BYD Qin Pro, no collision history. Dashboard suddenly displayed airbag fault. Measured passenger-side second-stage pretensioner resistance as infinite (OL). Disassembly found open circuit in pretensioner's internal igniter (internal fault). Replaced OEM seatbelt assembly (including pretensioner), used diagnostic tool to perform 'Replace Airbag ECU/Component' coding and matching procedure, cleared fault codes, system returned to normal.
BYD DTC AI Analysis

Aftermarket seats crushed the wiring harness

✓
2019 Song MAX. Owner fitted aftermarket electric seats, triggering DTC B179A. Inspection found seat rail mounting bolts had crushed the pretensioner harness during modification, severing internal copper strands while outer insulation appeared undamaged. Stripping back the wiring revealed three copper conductors completely broken. Repaired the damaged harness, rerouted clear of seat moving mechanisms, and protected with corrugated tubing. Fault cleared and owner counselled regarding modification risks.
BYD DTC AI Analysis

B-pillar trim incorrectly fitted, crushed wiring harness

✓
2021 Tang. Passenger airbag warning light on after accident repair. Found DTC B179A. Removed B-pillar trim and found the wiring harness misrouted during the previous repair; trim clips were pressing directly on the pretensioner harness, nearly severing it. Replaced the damaged harness section, rerouted per standard procedure, and ensured adequate slack for seatbelt travel. Fault resolved.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.