AU
B176F

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

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 Seal U 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. The vehicle should be inspected and repaired by an authorised dealer. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Long-term friction and pinching from fore-and-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 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.
  • 4Damage from improper modifications, such as piercing the wiring harness when installing seat heating pads, ambient lighting, or audio equipment, or using excessively long mounting screws that penetrate the wiring harness insulation.
  • 5SRS ECU internal driver circuit fault (such as MOSFET breakdown) causing false detection, or intermittent short circuit (poor connection) between the wiring harness and body ground point.
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 at the time of the fault, and 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 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: >1 MΩ (infinite). Continuity indicates a short to ground in the wiring harness. Measure the resistance of the pretensioner itself. Normal: 2.0–3.0 Ω. Resistance <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. Inspect and clean the connector terminals, and apply a 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 specification (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 check: 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; in actual repairs, verifying no fault codes are present is usually sufficient).
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 Seal U Fault Codes
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.