AU
B176A

DTC B176A indicates the SRS (Supplemental Restraint System) detects a resistance of 0 ohms in the left rear seat belt pretensioner circuit — Seal U

Safety System

DTC B176A indicates the SRS (Supplemental Restraint System) detects a resistance of 0 ohms in the left rear seat belt pretensioner circuit.

Normally, as a pyrotechnic device, the pretensioner resistance ranges from 1.5–3.0 Ω (depending on vehicle configuration).

A resistance of 0 indicates a short in the circuit, typically a short to ground or an internal short within the pretensioner.

This causes the Airbag Control Unit (ACU) to identify a pretensioner circuit fault.

During a collision, the left rear seat belt pretensioner may fail to deploy, severely compromising rear occupant restraint protection.

This fault also illuminates the instrument cluster SRS warning light and may lock the entire airbag system, preventing other airbags from deploying normally.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Short circuit to ground in the left rear seat belt pretensioner wiring harness (long-term chafing from seat adjustment damages the wiring harness insulation inside the B-pillar trim)
  • 2Internal short circuit, water ingress corrosion, or poor terminal contact in the pretensioner connector (usually a yellow waterproof connector) resulting in a short circuit.
  • 3Seat belt pretensioner assembly internal short circuit (internal igniter bridge wire short circuit or pyrotechnic component fault)
  • 4An internal detection circuit fault in the SRS control unit (ACU) causes a false resistance reading of 0.
  • 5Vehicle wading, deep interior cleaning, or a sunroof leak causes water ingress and a short circuit in the connector below the B-pillar.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Locate the component: Remove the left rear B-pillar lower trim panel. Find the left rear seat belt pretensioner (usually integrated into the base of the seat belt retractor) and its yellow connector.
  • 3
    Isolation measurement: Disconnect the pretensioner connector. Use a multimeter to measure the resistance directly between the two terminals on the pretensioner body. Check if the resistance is 0 Ω (normal: 1.5-3.0 Ω).
  • 4
    Harness inspection: If component resistance is normal, measure the resistance from both harness-side terminals to body ground and check for a short to ground; also check for a short circuit between the harness wires.
  • 5
    Visual inspection: Inspect the wiring harness routing down the B-pillar. Focus on wear-prone areas such as near the seat rails and under the carpet. Check the wiring harness for damage, crushing, or signs of water ingress.
  • 6
    Connector treatment: If water ingress or corrosion is present, clean the connector with electrical contact cleaner, dry it, and apply conductive grease. Replace the waterproof sealing ring if necessary.
  • 7
    Component replacement: If inspection confirms a short circuit in the pretensioner body, replace the left rear seat belt assembly (the pretensioner is usually not supplied separately). If the wiring harness is damaged, repair or replace the wiring harness.
  • 8
    System reset: Restore all connections, turn on the power, and use VDS or a dedicated diagnostic tool to clear the fault code. Perform the SRS system self-check procedure. Confirm B176A does not return and the SRS warning light is off.
Real-World Cases
BYD DTC AI Analysis

Worn B-pillar wiring harness caused pretensioner short circuit

✓
A 2020 BYD Qin Pro EV had the SRS warning light constantly illuminated. Technicians retrieved DTC B176A. Removing the left rear B-pillar trim revealed the seatbelt pretensioner harness rubbing against the seat rails below the B-pillar. Long-term friction had worn through the insulation, exposing the copper wire and causing a short to ground against the body shell. Resistance measured 0Ω. Repair: Repaired the damaged harness (rewrapped with insulation tape and sleeved with corrugated tubing), adjusted the harness position to prevent seat interference, and replaced the damaged pretensioner connector terminals. After clearing the fault codes, the SRS system returned to normal.
BYD DTC AI Analysis

Pretensioner connector shorted from water ingress after wading

✓
2019 BYD Song MAX. Owner reported the SRS warning light illuminated suddenly after driving through a flooded section. Fault code B176A. Inspection found damp carpet in the left rear. Removed the B-pillar trim to find clear water staining inside the yellow pretensioner connector; terminals were oxidised and blackened, shorting the signal wire to ground. Resistance measured 0 ohms. Repair: Dried the wiring harness and connector with compressed air, cleaned the oxidised terminals with electronic cleaner, applied waterproof conductive grease, and replaced the connector seal. Traced the water ingress to a blocked sunroof drain tube; cleared the blockage to resolve the fault.
BYD DTC AI Analysis

Internal short circuit in pretensioner after accident repairs

✓
A 2021 BYD Tang was involved in a minor collision on the left rear side. After accident repairs, the instrument cluster displayed DTC B176A. Inspection showed no external damage to the left rear seatbelt pretensioner, but resistance measured 0Ω (normal is approximately 2.0Ω). Disassembly revealed the internal igniter's bridge wire had shorted from the collision impact. Pretensioners are single-use safety devices; the internal short was unrepairable even though the unit did not deploy. Fix: Replaced the left rear seatbelt assembly (includes pretensioner), ran the seatbelt pretensioner resistance learn procedure with a diagnostic tool (required on some models), cleared the fault code. System self-test passed.
BYD DTC AI Analysis

Intermittent short circuit causing intermittent B176A

✓
A 2019 BYD Yuan EV came in with the SRS warning light intermittently illuminating. Scanning revealed historic DTC B176A; current status was normal. The technician found the left rear seatbelt pretensioner connector slightly loose—driving on bumpy roads caused the terminals inside to intermittently contact and short. Inspection also revealed the connector locking tab broken, resulting in poor sealing. Repair: Replaced the pretensioner wiring harness connector with a new unit featuring the locking tab, re-crimped the terminals, and ensured a secure connection. Used an oscilloscope to monitor the pretensioner circuit resistance waveform and confirmed no abnormal fluctuations before delivery. One-week follow-up confirmed the fault had not reoccurred.
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.