AU
B176F

This fault code indicates an abnormally low-resistance connection to body ground (GND) in the left rear seat belt pretensioner drive circuit — Atto 3

Safety System

This fault code indicates an abnormally low-resistance connection to body ground (GND) in the left rear seat belt pretensioner drive circuit.

As a key actuator in the SRS (Supplemental Restraint System), the pretensioner typically uses a pyrotechnic or motor-driven design.

During a collision, it rapidly retracts the seat belt webbing by igniting a gas generator or driving a motor, eliminating slack between the occupant and the seat belt.

A short to ground means the positive circuit between the SRS ECU and the pretensioner (typically high-level triggered) shorts to the vehicle chassis ground, with resistance falling below the calibrated threshold (generally <2Ω).

Upon detecting this fault, the SRS ECU immediately enters fail-safe mode, cuts power to the circuit to prevent accidental deployment or wiring overheating, and illuminates the airbag warning lamp.

Consequently, the left rear seat loses pretensioner protection during a collision, and the occupant risks secondary impact injuries due to seat belt slack.

The short-circuit current may also overheat and damage the SRS ECU driver chip, compromising the normal operation of the entire airbag system.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Long-term fore-aft seat movement chafes and crushes the wiring harness under the left rear seat or at the B-pillar, damaging the insulation and causing the copper core to directly contact the vehicle body metal and short to ground.
  • 2Internal fault in the seat belt pretensioner unit: the squib resistance wire shorts to the metal housing. Moisture ingress, aging, or manufacturing defects in the pretensioner usually cause this.
  • 3After vehicle wading, flooding, or floor washing, water enters and corrodes the pretensioner connector (usually located under the seat or at the base of the B-pillar), forming an electrolytic conductive path between the terminals.
  • 4Non-professional modifications causing damage, such as piercing the wiring harness when installing seat heating pads, ambient lighting, or audio equipment, or penetrating the wiring harness insulation with excessively long mounting screws.
  • 5SRS ECU internal driver circuit fault (e.g., MOSFET breakdown) causing false detection, or intermittent short circuit (poor connection) between the wiring harness and body ground.
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the 12V low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 2
    Fault Confirmation and Freeze Frame Analysis: Connect the BYD dedicated diagnostic tool (VDS2000/3000). Read the freeze frame data for DTC B176F. Record the vehicle speed, ambient temperature, and voltage when the fault occurred. Determine if the fault is intermittent.
  • 3
    Visual inspection: Remove the left rear door sill trim panel and lower B-pillar trim panel. Inspect the pretensioner connector (usually marked yellow) for looseness, water ingress, or corrosion. Inspect the floor wiring harness for wear, damaged insulation, or pressure marks.
  • 4
    Circuit isolation test: Disconnect the SRS ECU and left rear pretensioner connectors. Use a multimeter to measure the resistance to ground on the pretensioner-side wiring harness. Standard value: >1 MΩ (infinite). Continuity indicates a short to ground in the wiring harness. Measure the resistance of the pretensioner itself. Standard value: 2.0-3.0 Ω. A resistance of <1 Ω or continuity to ground indicates an internal short circuit in the pretensioner.
  • 5
    Wiring harness repair: If the wiring harness is damaged, repair it using heat-shrink tubing and waterproof tape, or replace the damaged floor wiring harness assembly. Check and clean the connector terminals, and apply a conductive protectant if necessary.
  • 6
    Component replacement: If the pretensioner unit has a short circuit, replace the left rear seat belt assembly (including the pretensioner). The new part resistance value must fall within the standard range (2.0±0.2Ω) and match the original vehicle (distinguish between pyrotechnic and motor-driven types).
  • 7
    System reset and calibration: Reconnect all connectors, reconnect the battery, clear fault codes using the diagnostic tool, perform an SRS system self-test and configuration coding, and verify the system generates no new fault codes.
  • 8
    Function verification: Perform a static test (use the diagnostic tool to run an actuation test and observe the pretensioner resistance and status in the data stream) and a dynamic test (simulate a crash signal to check system response; actual repairs typically only require confirming no fault codes are present).
Real-World Cases
BYD DTC AI Analysis

Song MAX: Intermittent B176F after water submersion

✓
Vehicle drove through water approximately 30 cm deep. One week later, the instrument cluster intermittently displayed an SRS warning. Diagnosis found DTC B176F as an intermittent fault; freeze frame data indicated 100% humidity. Removed the left rear seat and found the wiring harness connector seal underneath had deteriorated, allowing water in. Terminals developed green copper corrosion and shorted to ground. Replaced the connector and waterproofed the area. Fault resolved.
BYD DTC AI Analysis

Tang DM seat modification crushed wiring harness

✓
When installing aftermarket aviation seats, mounting bolts that were too long pressed through the floor wiring harness. This damaged the insulation on the pretensioner power supply wire, causing it to contact the seat bracket. The DTC set with the seat secured but cleared when the seat was moved. Found the harness damaged at the seat rail mounting point. Repaired the harness and shortened the mounting bolts.
BYD DTC AI Analysis

Internal short circuit in the Yuan EV pretensioner assembly

✓
Vehicle had no collision history, but B176F persisted and would not clear. Disconnected the pretensioner connector and measured infinite harness-to-ground resistance (normal), but the pretensioner body plug showed continuity to the metal bracket. Replaced the left rear seat belt assembly (including pretensioner). New part measured 2.1Ω and showed no continuity to ground. Fault code cleared and has not returned.
BYD DTC AI Analysis

Qin Pro B-pillar wiring harness chafed and shorted to ground

✓
At 60,000 km, frequent opening and closing of the left rear door caused the B-pillar wiring harness to chafe against the body sheet metal, wearing through the insulation and exposing the copper core to the vehicle body. This caused the SRS light to flicker on rough roads. Removing the B-pillar trim revealed damaged harness protection. Re-wrapped the wiring and fitted a rubber protective sleeve. Fault eliminated.
BYD DTC AI Analysis

SRS ECU false positive fault

✓
The vehicle had no physical damage. Pretensioner wiring harness and unit measured normal, but the DTC kept recurring. Suspected internal ECU drive circuit fault. Replaced the SRS ECU with an identical unit and recoded it; fault cleared completely. Factory testing of the original ECU revealed internal MOSFET breakdown causing false short-to-ground detection.
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.