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B176B1A

DTC B176B1A indicates the left rear seat belt pretensioner circuit resistance falls below the standard threshold set by the SRS control unit (ACU) (typically 1 — Atto 3

Safety System

DTC B176B1A indicates the left rear seat belt pretensioner circuit resistance falls below the standard threshold set by the SRS control unit (ACU) (typically 1.5–3.0 Ω; the fault triggers below the lower limit).

This is an SRS hard fault, indicating a potential or actual short circuit in the pretensioner igniter circuit.

As a key passive safety system actuator, the pretensioner uses electrical current to trigger the igniter.

This ignites the gas generator to tighten the seat belt during a collision (within approximately 15–20 ms).

Low resistance may cause: 1) Unintended deployment (static electricity or electromagnetic interference causing accidental ignition); 2) The ACU to disable this trigger circuit in fail-safe mode, preventing seat belt pretensioning during a collision; 3) The ACU to lock out the entire SRS system if resistance drops near 0 Ω, disrupting the multi-airbag coordinated deployment strategy.

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Cases Logged
Real-World Cases
BYD DTC AI Analysis

Water ingress under left rear seat caused pretensioner short circuit

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2019 BYD Qin PRO DM. Owner reported the airbag warning light stayed on constantly. Read DTC B176B1A. Inspection found the left rear carpet damp. Disassembly revealed obvious water stains inside the yellow 2-pin SRS connector under the left rear seat; electrolytic corrosion caused a micro-short between terminals, measuring 0.8Ω. Cause: The left rear door seal had deteriorated, allowing rainwater to seep in and accumulate at the lowest point of the seat rail. Replaced the left rear seatbelt pretensioner assembly (including retractor), treated the corroded terminals in the wiring harness, replaced the door seal, and dried the cabin. No recurrence in three months of follow-up.
BYD DTC AI Analysis

Aftermarket heated seats caused impedance anomaly

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2018 Qin PRO petrol. B176B1A set within one week of aftermarket rear seat heater installation at a non-authorized workshop. Technicians found the installer had spliced the heating pad power feed into the seatbelt pretensioner harness in parallel, dropping total SRS circuit resistance to 1.2Ω. The ACU detected resistance deviation exceeding 25% and triggered the fault code. Repair: Removed the unauthorized harness, repaired original wiring insulation with double-layer heat shrink tubing, and restored factory connectors. Explained to the customer that the SRS system strictly prohibits parallel loads; recommended an independent power supply for seat heating.
BYD DTC AI Analysis

ACU internal sampling resistor drift causes false fault

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A Qin PRO DM with 60,000 km showed intermittent B176B1A faults. Left rear pretensioner resistance measured 2.1Ω (normal) and harness insulation was good, yet the fault triggered on rough roads. Oscilloscope monitoring revealed abnormal voltage fluctuations at the ACU sampling terminal. After replacing the ACU (airbag control unit), the fault disappeared. The reference resistor in the Analog Front End (AFE) chip had drifted from thermal cycling, shifting the sampling reference for the left rear channel. When hardware tests normal but the fault code keeps returning, suspect the ACU itself.
BYD DTC AI Analysis

B-pillar wiring harness chafed, short to ground

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2019 Qin Pro set DTC B176B1A after accident repairs (left rear door replacement). Inspection found the B-pillar trim panel was installed with the harness improperly secured. The seatbelt pretensioner wiring (yellow corrugated tubing) was pinched between the door outer panel and B-pillar reinforcement. Repeated door closing vibrations chafed through the insulation, exposing the copper core and creating a low-resistance path to ground (measured 12Ω). Repair: Cut out the damaged section, soldered in an extension, and applied double insulation. Rerouted and secured the harness per standard wiring paths, ensuring >20mm clearance from sharp edges. 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.