AU
B176B-00

This DTC indicates the SRS (Supplemental Restraint System) control unit detects the left rear seat belt pretensioner ignition circuit resistance is below the normal system-calibrated threshold (the standard value is typically 2 — Seal U

Safety System

This DTC indicates the SRS (Supplemental Restraint System) control unit detects the left rear seat belt pretensioner ignition circuit resistance is below the normal system-calibrated threshold (the standard value is typically 2.0Ω±0.3Ω; values below 1.0Ω trigger this code).

The pretensioner uses a pyrotechnic igniter to tighten the seat belt during a collision, removing slack between the webbing and the occupant.

Low resistance indicates a potential short circuit.

Possible causes include a wiring harness short to ground, bridged connector pins, an internal short in the pretensioner igniter, or a faulty internal sampling circuit in the SRS control unit.

This fault forces the airbag system into a degraded mode.

The left rear pretensioner may fail to deploy during a collision or deploy unintentionally without a collision, severely compromising passive safety.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Water ingress, oxidation, or bent pins at the left rear seat belt pretensioner connector (usually located inside the lower B-pillar trim panel or under the seat) causing a short circuit.
  • 2Damaged wiring harness insulation between the pretensioner and the SRS control unit contacts vehicle body metal, causing a short to ground. The harness is especially prone to wear at the seat slide rail or B-pillar wiring hole.
  • 3Aging or damage to the internal pretensioner squib causes an internal short circuit, resulting in permanently low resistance.
  • 4Foreign objects (such as metal toys or liquids) corroded or crushed the wiring harness under the rear seat, causing a short circuit.
  • 5False alarm caused by a faulty internal A/D conversion circuit or sampling resistor in the SRS control unit (uncommon, but requires inspection)
What To Do
  • 1
    Use a dedicated diagnostic tool (such as BYD ED400 or Launch X431) to read the complete SRS fault codes, confirm whether B176B-00 is a current or history code, and record the freeze frame data.
  • 2
    Perform the safe power-down procedure: Turn off the ignition switch, disconnect the negative battery terminal, and wait at least 3 minutes to fully discharge the SRS system capacitors and prevent accidental deployment.
  • 3
    Remove the left rear B-pillar lower trim panel (or seat back side panel), locate the yellow seat belt pretensioner connector, and visually inspect for signs of water ingress, green corrosion, bent pins, or loose connections.
  • 4
    Test using the dedicated SRS dummy load: Disconnect the pretensioner connector and connect the dummy load to the wiring harness side (leading to the SRS control unit). The system should display normal resistance. If a direct resistance measurement at the wiring harness side is abnormally low (<1Ω), diagnose a wiring harness short circuit.
  • 5
    Inspect insulation integrity along the pretensioner wiring harness route (via the lower B-pillar and floor wiring channel to the centre tunnel). Closely inspect the wiring harness near the seat slide rail for wear or chafed insulation caused by long-term seat adjustment.
  • 6
    If the wiring harness tests normal, the pretensioner unit is faulty. Replace the left rear seat belt assembly (including the pretensioner retractor). Never remove the pretensioner module separately.
  • 7
    After installing the new component, restore all connections, reconnect the battery, use the diagnostic tool to clear the fault code, and perform the 'SRS system self-check' or 'igniter resistance learning' procedure.
  • 8
    Perform a road test simulation (including bumpy roads) to confirm the airbag warning light turns off and the system generates no new fault codes. Finally, reinstall the interior trim panel.
Real-World Cases
BYD DTC AI Analysis

Water ingress in the B-pillar connector caused a short circuit.

✓
A 2017 Qin EV300 came in with the airbag warning light on after driving in heavy rain. Read DTC B176B-00 (current). Removed the lower left rear B-pillar trim and found standing water inside the yellow pretensioner connector, along with green corrosion between the pins. Multimeter showed 0.6Ω to ground at the harness side, confirming a short caused by water intrusion. Cleaned the connector thoroughly with electronic cleaner, dried it, applied conductive grease for waterproofing, and reconnected. The code cleared and the system returned to normal. Recommend inspecting the B-pillar trim seal for deterioration that may be allowing water ingress.
BYD DTC AI Analysis

Wiring harness chafed at seat track, short to earth

✓
Airbag warning light illuminated intermittently after frequent adjustment of the left rear seatback angle. DTC B176B-00 stored as intermittent. Inspection found the pretensioner harness insulation chafed through at the seat hinge-to-slide rail junction, with exposed copper wire contacting the seat frame and causing a short to ground. Repaired by cutting out the damaged harness section, soldering in an extension wire, and protecting with corrugated tubing. Rerouted the harness away from the seat movement path, ensuring sufficient slack without contacting metal components. Fault resolved.
BYD DTC AI Analysis

Internal short circuit in pretensioner after accident repair

✓
A Qin 100 persistently set DTC B176B-00 after accident repair and the code would not clear. Inspection found the left rear seat belt had been replaced with a salvage part. After ruling out wiring harness faults using a dedicated load simulator, we measured the pretensioner body resistance directly: 0.4Ω, far below specification. This confirmed an internal short in the igniter. We replaced the left rear seat belt assembly with a new genuine unit (including pretensioner), performed 'Configure New Module' and 'System Calibration' via the diagnostic tool, and cleared the fault code. Never use salvage parts from accident vehicles or measure airbag/pretensioner resistance directly; always use the substitute load method.
Other Seal U 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.