AU
B176C

DTC B176C indicates the left rear seat belt pretensioner circuit resistance exceeds the normal threshold set by the SRS ECU (typically >3 — Seal 6 EV

Safety System

DTC B176C indicates the left rear seat belt pretensioner circuit resistance exceeds the normal threshold set by the SRS ECU (typically >3.5-4.0Ω; normal value is 2.0-3.0Ω).

The pretensioner is a pyrotechnic safety device containing an igniter and a gas generator.

Excessive resistance indicates a high resistance or open circuit condition within the circuit.

Consequently, during a collision, the SRS ECU may fail to ignite the pretensioner charge.

This failure prevents the seat belt from tightening, increases occupant forward displacement, and severely reduces crash protection.

Additionally, the SRS system enters degraded mode, illuminates the airbag warning lamp continuously, and may disable the related side airbag function on certain models.

The B176C fault code on the Seal 6 EV indicates excessive resistance in the left rear seat belt pretensioner circuit, which may stop the pretensioner from tightening the belt in a crash. Severity is medium, but SRS protection may be reduced and the airbag warning light may stay on. Common causes include a faulty pretensioner igniter or poor/corroded connector contact. 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 6 EV
  • 1Aging or open circuit in the left rear seat belt pretensioner internal igniter tube: Prolonged disuse or moisture exposure oxidizes the internal bridge wire, gradually increasing resistance over time until it exceeds the threshold.
  • 2Poor connector contact: The pretensioner connector near the B-pillar or C-pillar (usually marked SR11 or P11) is loose, oxidized, corroded by water ingress, or has backed-out terminals, causing increased contact resistance.
  • 3Wiring harness damage: Frequent opening and closing of the left rear door partially broke the internal copper strands of the hinge wiring harness, or removing and installing the B-pillar trim panel pinched the wiring harness, creating a high-resistance path.
  • 4Poor ground connection between the pretensioner and vehicle body: A loose or oxidized pretensioner housing ground point causes abnormal circuit resistance (for low-side drive pretensioner circuits).
  • 5SRS ECU internal sampling circuit fault: ECU internal A/D converter or sampling resistor fault falsely reports high resistance (rule out by cross-checking).
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 3 minutes to fully discharge the SRS system capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect the diagnostic tool and read DTCs. Confirm B176C is a current fault (Active), not a history fault. Record the resistance value in the freeze frame data.
  • 3
    Visual inspection: Remove the left B-pillar lower trim panel. Inspect the pretensioner connector for looseness, signs of water ingress, pin corrosion, or backed-out pins. Clean and reconnect if necessary.
  • 4
    Pretensioner resistance measurement: Disconnect the connector. Use a digital multimeter to directly measure the resistance across the two pretensioner terminals. The normal range is 2.0-3.0Ω. If the reading is >4Ω or displays OL (open circuit), replace the left rear seat belt pretensioner assembly (usually integrated with the seat belt retractor).
  • 5
    Harness continuity test: Measure harness resistance between the pretensioner connector and the SRS ECU (usually under the centre console or in the front compartment). Resistance must be <1.0Ω. If resistance is too high, repair or replace the harness.
  • 6
    Insulation check: Measure the pretensioner wiring harness resistance to ground. It must be >1 MΩ. If a short to ground exists, repair the damaged section of the wiring harness.
  • 7
    Cross-check: If all above checks are normal, test with a known good pretensioner. If the fault code clears, this confirms an internal pretensioner fault. Otherwise, check the SRS ECU.
  • 8
    System reset: Install all components, connect the battery, and clear the fault codes. Turn the ignition switch to the ON position and verify the SRS warning light turns off after 6 seconds. Perform a road test to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

B-pillar trim removed and refitted with connector not locked, causing high resistance

✓
A 2020 BYD Song MAX triggered DTC B176C following left rear door respray. The white 4-pin pretensioner connector wasn't fully locked after the B-pillar trim was removed and refitted—just loose. Reseated the plug until it clicked; resistance returned to 2.3Ω. Cleared the code; SRS light went out. Common after accident repairs since the connector hides behind the trim and is easy to miss.
BYD DTC AI Analysis

Electrical connectors oxidised and corroded after water submersion

✓
A 2019 Yuan EV's airbag warning light came on one day after driving through heavy floodwater. Scan showed DTC B176C. Removed the left rear floor trim and found water in the seatbelt pretensioner harness connector; the copper pins showed green oxidation. Cleaned the connector with electrical contact cleaner, applied conductive grease, and reinstalled it. The fault cleared temporarily but returned a week later. Replaced the pretensioner harness connector and waterproofed it—problem solved. Inspect SRS system connector sealing immediately on any flood-damaged vehicle.
BYD DTC AI Analysis

Pretensioner internal igniter open circuit due to aging

✓
A 2019 BYD Qin gasoline variant (commercial fleet vehicle, 280,000 km) logged active fault code B176C. Resistance at the pretensioner connector read OL (open circuit). Disassembly revealed a fractured igniter bridge wire. Replaced the left rear seatbelt assembly (including pretensioner); fault cleared. Root cause: Metal fatigue in the igniter from prolonged intensive use and wide cabin temperature swings. High-mileage vehicles require regular SRS component inspections.
BYD DTC AI Analysis

Wiring harness internal break at left rear door hinge

✓
A 2021 BYD Tang DM exhibited intermittent SRS warning light illumination when opening or closing the left rear door. The scan tool displayed B176C intermittent fault. Static resistance measured normal, but resistance fluctuated when repeatedly cycling the door. Stripping back the wiring harness protective sleeve at the left front door hinge revealed two copper wires partially fractured, with only a few thin strands remaining connected. Replaced the wiring harness section from body to door (including pre-tensioner circuit). Repeated door cycling confirmed stable resistance and resolved the fault. This is a common failure point on BYD models; frequent door operation causes wiring harness fatigue.
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.