AU
B176F-00

DTC B176F-00 indicates the SRS (Supplemental Restraint System) ECU detects an abnormal electrical connection between the left rear seat belt pretensioner drive circuit and the vehicle power supply (B+) — Seal U

Safety System

DTC B176F-00 indicates the SRS (Supplemental Restraint System) ECU detects an abnormal electrical connection between the left rear seat belt pretensioner drive circuit and the vehicle power supply (B+).

The pretensioner consists of an igniter and a gas generator, with a normal resistance of 2.0-3.0Ω.

Damaged wiring harness insulation, misaligned connector pins, or an internal pretensioner short circuit cause the ECU to detect an abnormally high circuit voltage (approaching 12V battery voltage) and trigger this DTC.

This fault may result in: 1) Failure of the left rear pretensioner to deploy during a collision, compromising occupant protection. 2) Unintended pretensioner deployment in extreme cases, causing occupant injury. 3) The SRS entering fail-safe mode, disabling all vehicle airbags.

The B176F-00 fault code on the Seal U indicates a high-severity SRS fault where the left rear seat belt pretensioner circuit has an abnormal connection to battery power. Common causes include damaged wiring insulation under the left rear seat or near the B-pillar, or corrosion, water ingress, or bent pins in the pretensioner connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Worn insulation on the pretensioner wiring harness under the left rear seat or near the B-pillar contacts the body power wire (constant power or ignition power), causing a short circuit.
  • 2Water ingress, oxidation, or bent pins in the pretensioner connector (usually located under the seat or inside the B-pillar trim) causing a short circuit between the power and signal terminals.
  • 3Igniter coil insulation failure inside the left rear seat belt pretensioner assembly causes an internal short to power.
  • 4During vehicle modifications (such as adding seat heating or ambient lighting), a technician mistakenly connects the pretensioner wiring harness in parallel with a power wire or pierces the harness insulation.
  • 5Internal driver circuit fault in the SRS ECU (MOSFET breakdown) causing false short-circuit detection (low probability)
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the left rear seat and lower B-pillar trim panel. Check the pretensioner wiring harness (usually in a yellow sleeve) for wear, crushing, or burn marks. Focus on the wiring harness within the seat slide rail movement range.
  • 3
    Connector check: Disconnect the pretensioner connector and check the pins for corrosion, water ingress, or deformation. Measure the voltage to ground at the connector-side harness terminals to confirm if an abnormal 12V voltage is present.
  • 4
    Component test: Use a digital multimeter to measure the resistance of the pretensioner body (must remain stable between 2.0-3.0Ω). If the resistance is 0Ω or infinite, or has continuity to the power supply, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If the wiring harness is damaged, repair it using high-temperature insulating tape (or replace the entire harness section). Keep the harness at least 10 cm away from the power cable to avoid electromagnetic interference.
  • 6
    System reset: Reconnect all connectors and the battery. Use VDS2000 or the BYD dedicated diagnostic tool to clear the fault codes, then perform 'SRS system self-check' and 'configuration write' (if installing a new component).
  • 7
    Function verification: Perform an ignition cycle test to confirm the fault code does not reappear, observe if the airbag warning light turns off after the self-check, and finally perform a road test.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450 left rear seat rail chafed through wiring harness causing short circuit

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2018 Qin EV450, 42,000 km. Constant airbag warning light. DTC B176F-00. The pretensioner harness under the left rear seat had chafed against the slide rail mounting bolt edge during fore/aft adjustment, wearing through the insulation. The copper core contacted the seat heater power wire (red, 12V constant). Replaced the entire yellow harness from the floor harness to the pretensioner (PN 4C-5823456) and added retaining clips to prevent contact with metal edges. Cleared the DTC; system returned to normal.
BYD DTC AI Analysis

Qin 100 rear seat water ingress caused connector short circuit

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2017 BYD Qin 100. After heavy rain, water pooled in the left rear footwell and wasn't cleaned up. DTC B176F-00 set intermittently. Tore down the B-pillar and found the 2-pin pre-tensioner connector underneath had taken on water. Electrolytic corrosion between the pins produced verdigris, dropping insulation resistance between the power and pre-tensioner drive pins below 200 Ω (normal: infinite). Fix: Cleaned the connector with electronic cleaner, blew it dry, applied conductive grease, replaced the waterproof seal, and cleared the door drain holes to stop it happening again.
BYD DTC AI Analysis

Incorrect wiring of aftermarket seat heater caused fault

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The owner had a heating pad installed on the left rear seat at a third-party workshop. The technician incorrectly spliced the heating pad power feed into the pretensioner wiring harness, mistaking the yellow wiring for the seat power supply. This caused the pretensioner circuit to connect directly to 12V power. The vehicle immediately set code B176F-00 at power-up, and the code could not be cleared. Repair actions: Removed the unauthorised modification, replaced the damaged pretensioner (internal igniter likely damaged by high-voltage impact), restored the factory wiring layout, and explained to the owner that the SRS system prohibits unauthorised modifications.
BYD DTC AI Analysis

Pretensioner internal coil aged and short-circuited

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A Qin EV300 with 80,000 km and no accident history suddenly set DTC B176F-00. Harness visual inspection revealed no damage. With the connector disconnected, the harness side showed no short to power, but the pretensioner terminals measured 0.5Ω to case. Internal igniter coil insulation had degraded and shorted. Replaced the left rear seatbelt assembly (includes pretensioner, PN 4C-6912345). Fault resolved. Note: Pretensioners are single-use components; even without deployment, internal materials can degrade after long-term use.
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.