AU
B176B

This fault code indicates the airbag control unit (SRS ECU) detects the left rear seat belt pretensioner resistance is below the system threshold (typically below 2 — Seal U

Safety System

This fault code indicates the airbag control unit (SRS ECU) detects the left rear seat belt pretensioner resistance is below the system threshold (typically below 2.0 Ω; standard value: 2.0–3.0 Ω).

As a pyrotechnic safety device, the pretensioner contains a squib and a gas generator.

Resistance must remain within a strict range to ensure reliable deployment.

Low resistance indicates a short circuit risk, abnormally low resistance in the internal squib, or damaged wiring harness insulation reducing resistance between the positive and negative terminals.

This causes two severe consequences: first, during a collision, the pretensioner may fail to ignite and deploy, eliminating safety restraint protection for the left rear passenger; second, the system may misidentify the condition as a short circuit and disable the trigger circuit.

In extreme cases, the system activates fault protection mode, affecting the entire SRS operation.

This fault illuminates the airbag warning light continuously and requires immediate repair.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Moisture ingress, aging, or an internal short circuit in the pretensioner igniter causes the resistance value to fall below the standard range (<2.0Ω).
  • 2Long-term fore-and-aft seat adjustment chafes the under-seat wiring harness, damaging the insulation and causing a short circuit between wires.
  • 3Water ingress, oxidation, corrosion, or bent pins making contact at the left rear seat belt pretensioner connector (usually located under the seat or lower B-pillar) cause abnormal continuity.
  • 4After vehicle wading, interior deep cleaning, or a sunroof leak, moisture enters the pretensioner connector or body, reducing resistance.
  • 5SRS ECU internal detection circuit fault (less common; confirm only after ruling out wiring and component faults)
What To Do
  • 1
    Safety preparation: Turn the power switch to OFF, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Check the left rear seat belt pretensioner connector (located under the seat or inside the B-pillar trim panel) for looseness, water ingress, corrosion, deformed pins, or green rust.
  • 3
    Pretensioner resistance measurement: Disconnect the pretensioner harness connector. Use a multimeter to measure the resistance directly between the two pins on the pretensioner. Standard resistance is 2.0-3.0 Ω. If the resistance is below 1.5 Ω or close to 0 Ω, the pretensioner has an internal fault. Replace the assembly.
  • 4
    Harness continuity and insulation test: Measure resistance from the harness side to ground (must be greater than 1MΩ to rule out a short to ground). Measure continuity between both ends of the harness (resistance between the pretensioner connector and the SRS ECU must be less than 1Ω). Check the harness for pinching or damage.
  • 5
    Swap test (optional): If both left and right rear pretensioners are accessible, swap the left and right pretensioner connectors and read the fault codes. If the fault code follows the component (changes to a right rear fault), the pretensioner is faulty. If the fault code remains B176B, the fault is in the wiring harness or ECU.
  • 6
    Repair/Replace: Based on inspection results, replace the left rear seat belt pretensioner assembly, repair damaged wiring harnesses, and clean or replace corroded connectors. The pretensioner is a single-use pyrotechnic device. Never directly measure a live pretensioner using a multimeter resistance setting.
  • 7
    System reset and verification: Reconnect the battery. Use the dedicated diagnostic tool to clear the fault codes. Switch the power to the ON position. Wait 20 seconds for the system to complete its self-check. Confirm the airbag warning light turns off and the diagnostic tool shows no current fault codes (Active Codes).
Real-World Cases
BYD DTC AI Analysis

Water intrusion corroded seat connectors, dropping resistance below normal.

✓
After heavy rain, a 2019 BYD Song MAX drove through standing water and the SRS warning light stayed on. Fault code B176B-00 registered: left rear seatbelt pretensioner resistance low. Technicians found the carpet under the left rear seat damp. They removed the pretensioner connector and found water stains and green copper corrosion inside, with slight continuity between the pins. After cleaning and drying the connector, the pretensioner measured normal resistance (2.3Ω), but the harness side showed abnormal resistance to ground. They replaced the connector and repaired the water-damaged harness. The fault cleared.
Original source ↗
BYD DTC AI Analysis

Frequent seat adjustment caused wiring harness chafing and short circuit

✓
A 2021 BYD Tang. The owner reported the SRS warning light illuminated after repeatedly adjusting the left second-row seat. DTC B176B-00 stored. Inspection revealed the second-row seats are power-adjustable. The pretensioner wiring harness under the seat track had improper retention and chafed against components during seat movement. This wore through the insulation and caused an intermittent short between the two internal conductors. The technician re-wrapped the harness and repositioned the retaining clips so the wiring stays slack throughout the full range of seat travel. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Seat belt pretensioner internal squib resistance low due to aging

✓
A 2019 BYD Yuan EV with no collision history had the SRS warning light on and DTC B176B-00 set. Disconnected the left rear seatbelt pretensioner connector and measured the pretensioner resistance directly at 1.2Ω, below the 2.0Ω lower limit. Inspected the connector and wiring harness and found no faults. The pretensioner's internal squib deteriorated from prolonged high-temperature exposure (vehicle parked outdoors for extended periods), causing the internal chemical charge to degrade from moisture and alter its resistance characteristics. Replaced the left rear seatbelt pretensioner assembly (required removal of the B-pillar trim). Programmed and matched; fault resolved.
Original source ↗
BYD DTC AI Analysis

Water ingress after interior cleaning caused abnormal resistance

✓
A 2020 BYD Qin airbag warning light came on the day after an interior detail with heavy cleaner use on the seats. A diagnostic scan read DTC B176B-00. Inspection found cleaning fluid residue inside the left rear seatbelt pretensioner connector (under the seat), causing low resistance to ground (0.8kΩ). The technician thoroughly cleaned the connector with electrical contact cleaner, dried it with compressed air, and applied conductive protectant. Resistance returned to normal; after clearing the fault code, the warning light stayed off.
Original source ↗
BYD DTC AI Analysis

Connector not fully seated after accident repair

✓
A 2019 BYD Yuan sustained minor collision damage to the left rear. After replacing the left rear quarter panel, an SRS self-check returned fault code B176B-00. Inspection revealed that during left rear seat removal and refitting, the technician failed to fully seat the pre-tensioner connector and engage the locking tab, causing poor pin contact and high resistance. The technician re-seated the connector until the lock clicked, cleared the fault code, and restored normal operation. Always verify all SRS-related connectors are properly secured after accident repairs.
Original source ↗
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.