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 8

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.

The B176F fault code on the Atto 8 indicates a high-severity short to ground in the left rear seat belt pretensioner circuit. This can disable pretensioner protection and trigger the airbag warning light. Common causes include damaged wiring under the rear seat or near the B-pillar, or an internal pretensioner fault. Stop using the seat until inspected and visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Long-term friction and pinching 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 unit. The squib resistance wire shorts to the metal housing. Moisture ingress, aging, or manufacturing defects in the pretensioner usually cause this fault.
  • 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.
  • 4Damage from non-professional modifications, 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 fixing screws.
  • 5SRS ECU internal driver circuit fault (such as MOSFET breakdown) causing false detection, or intermittent short circuit (poor contact) 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 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. Check the pretensioner connector (usually marked yellow) for looseness, water ingress, or signs of corrosion. Check the floor wiring harness for wear, damaged insulation, or pinch marks.
  • 4
    Circuit isolation test: Disconnect the SRS ECU and left rear seat pretensioner connectors. Use a multimeter to measure the resistance to ground on the pretensioner-side wiring harness. Normal value: >1 MΩ (infinite). Continuity indicates a wiring harness short to ground. Measure the pretensioner body resistance. Normal value: 2.0-3.0 Ω. Resistance <1 Ω or continuity to ground indicates an internal pretensioner short.
  • 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 conductive protective agent if necessary.
  • 6
    Component replacement: If the pretensioner body has a short circuit, replace the left rear seat belt assembly (including the pretensioner). Verify the new part resistance is within the standard range (2.0±0.2Ω) and matches the original vehicle (distinguish between pyrotechnic and motor-driven types).
  • 7
    System reset and calibration: Reconnect all connectors, reconnect the battery, use the diagnostic tool to clear fault codes, perform the 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 the 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 usually 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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.