AU
B176F

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

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 — Qin Plus
  • 1Long-term friction and compression from fore-aft seat movement damages the wiring harness insulation under the left rear seat or at the B-pillar, causing the copper core to directly contact the vehicle body metal and short to ground.
  • 2Internal fault in the seat belt pretensioner assembly. The squib resistance wire short-circuits to the metal housing. Moisture ingress, aging, or manufacturing defects usually cause this.
  • 3Vehicle wading, flooding, or floor washing causes water to enter and corrode the pretensioner connector (usually located under the seat or at the base of the B-pillar), forming an electrolytic conductive path between the terminals.
  • 4Damage from non-professional modifications, such as piercing the wiring harness when installing seat heating pads, ambient lighting, or audio systems, 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, disconnect the negative terminal of the 12V low-voltage battery, 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 at the time of the fault, and determine if it is an intermittent fault.
  • 3
    Visual inspection: Remove the left rear door sill trim panel and lower B-pillar trim panel. Check the pretensioner connector (usually marked in yellow) for looseness, water ingress, or corrosion. Check the floor wiring harness for wear, damaged insulation, or compression marks.
  • 4
    Circuit isolation test: Disconnect the SRS ECU and left rear pretensioner connectors. Use a multimeter to measure the resistance to ground of the pretensioner-side wiring harness: normal value is >1MΩ (infinite); continuity indicates a wiring harness short to ground. Measure the resistance of the pretensioner itself: normal value is 2.0-3.0Ω; resistance <1Ω or continuity to ground indicates an internal short 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; apply a conductive protectant if necessary.
  • 6
    Component replacement: If the pretensioner has a short circuit, replace the left rear seat belt assembly (including the pretensioner). The new part resistance must be 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 the SRS system self-check 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 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 Qin Plus Fault Codes
B1108For 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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.