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B172B

DTC B172B indicates the SRS (airbag) control unit detects an open circuit or disconnected condition in the left middle-row side airbag module (typically located inside the left B-pillar trim or on the side of the left rear seat) — Atto 3

Safety System

DTC B172B indicates the SRS (airbag) control unit detects an open circuit or disconnected condition in the left middle-row side airbag module (typically located inside the left B-pillar trim or on the side of the left rear seat).

An abnormal resistance value in the circuit between the control unit and the airbag squib (typically infinite or outside the normal 2-3Ω range) causes the system to determine the airbag module is physically disconnected or internally open.

This fault prevents the left middle-row side airbag from deploying during a side-impact collision.

The SRS system may also enter a degraded protection mode, continuously illuminate the instrument panel airbag warning light, and restrict seat belt pretensioner function on some models.

3
Cases Logged
Real-World Cases
BYD DTC AI Analysis

BYD Tang B172B fault: Oxidised left middle row side airbag connector caused open circuit

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Symptoms: 2021 BYD Tang, airbag warning light stays on. DTC B172B stored (left second-row side airbag module disconnected). No collision history. Diagnosis: Inspected the airbag connector below the left B-pillar. Found green oxide inside with poor pin contact. Wiring harness continuity normal. Airbag module resistance 2.3Ω (normal). Repair: Cleaned connector pins with electronic cleaner, applied conductive grease, and reconnected. Cleared fault code; no recurrence. Analysis: Vehicle previously went through water. Moisture entered the B-pillar connector, causing oxidized high-resistance contact.
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BYD DTC AI Analysis

BYD Song MAX seat wiring harness chafing caused B172B

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Symptoms: 2019 Song MAX, airbag warning light illuminated intermittently while driving, diagnostic tool showed intermittent B172B fault. Diagnosis: Inspection found the SRS wiring harness beneath the left second-row seat interfering with the seat rail, with worn insulation causing the internal wires to intermittently open circuit. Repair: Repaired the damaged harness, wrapped it with corrugated tubing, and re-secured the harness routing to ensure safe clearance from the seat mechanism. Fault cleared.
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BYD DTC AI Analysis

BYD Qin Pro Left Second-Row Side Airbag Module Internal Fault Replacement Case

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Symptoms: SRS warning light stays on after starting the BYD Qin Pro. Fault code B172B will not clear. Diagnosis: Measured infinite resistance (open circuit) across left middle row side airbag module. Wiring harness continuity and connector contacts were good. Diagnosed an open circuit in the airbag module's gas generator igniter. Resolution: Replaced left middle row side airbag module assembly (transport safety precautions observed for new part). Used diagnostic scan tool to configure and match the system, then ran airbag self-test. Fault resolved.
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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.