AU
B176D

DTC B176D indicates the SRS (Supplemental Restraint System) ECU detects an open circuit in the left rear seat belt pretensioner circuit (infinite resistance), meaning the ECU cannot detect the pretensioner — Atto 3

Safety System

DTC B176D indicates the SRS (Supplemental Restraint System) ECU detects an open circuit in the left rear seat belt pretensioner circuit (infinite resistance), meaning the ECU cannot detect the pretensioner.

This typically indicates a broken circuit connection between the pretensioner and the ECU, or an internal open circuit within the pretensioner.

As a key passive safety actuator, the pretensioner rapidly tightens the seat belt via pyrotechnic deployment or motor operation during a collision, removing slack between the webbing and the occupant.

This fault disables the left rear seat pretensioner during a collision, increasing occupant injury risk.

The ECU continuously monitors the pretensioner circuit resistance (normal range: approx. 2.0-3.0Ω).

It sets a 'not present' fault when it detects a resistance >10Ω or a complete open circuit.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Loose or poor contact at the left rear seat belt pretensioner wiring harness connector (commonly occurs when failing to fully seat the rear seat after removal, or when a broken connector locking tab causes an intermittent connection).
  • 2Internal open circuit in the pretensioner unit (broken pretensioner squib wire or internal circuit board failure prevents the ECU from establishing a valid circuit)
  • 3Physical damage to the wiring harness (seat slide rail pinching the harness over time, or seat folding mechanism wearing through the harness insulation and breaking internal copper wires)
  • 4Connector pins corroded, oxidized, or backed out (liquid intrusion into the connector during rear area cleaning causes pin oxidation and excessive contact resistance)
  • 5SRS ECU internal detection circuit fault (damaged ECU sampling resistor or detection chip falsely reports a missing pretensioner; actual circuit is normal)
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS system capacitors and prevent accidental airbag deployment.
  • 2
    Initial visual inspection: Remove the left rear seat (usually requires removing the seat cushion retaining bolts). Verify the pretensioner connector (usually located inside the C-pillar trim panel or under the seat) is fully seated. Inspect the wiring harness for obvious damage or crush marks.
  • 3
    Connector reset and cleaning: Disconnect the pretensioner connector. Inspect the pins for oxidation, corrosion, or bending. Clean with electronic connector cleaner, then reconnect. Listen for a 'click' to confirm the lock engages.
  • 4
    Resistance measurement verification: Measure the pretensioner side resistance using a multimeter. Normal value: 2.1-2.9Ω (at 20°C). If the resistance is infinite, replace the pretensioner assembly.
  • 5
    Harness continuity check: Measure the resistance of the harness between the SRS ECU connector and the pretensioner connector. The resistance must be less than 1 Ω. Measure the insulation resistance to ground. The resistance must be greater than 1 MΩ. This rules out a harness open circuit or short to ground.
  • 6
    Replacement verification (cross-test): Swap the left rear and right rear pretensioner connectors (if vehicle configurations match). Observe if the fault code moves with the component to confirm whether the pretensioner or the wiring harness/ECU is faulty.
  • 7
    ECU software check: Use VDS2000 or a dedicated BYD diagnostic tool to check the SRS ECU software version. Upgrade to the latest version if necessary to rule out software false codes.
  • 8
    Repair verification: Reconnect the battery, clear the fault code, cycle the ignition switch to the ON position, and wait 20 seconds. Verify the SRS warning lamp turns off and no current B176D fault code is present. Perform a dynamic road test to verify.
Real-World Cases
BYD DTC AI Analysis

Left rear seat connector not reconnected after removal caused B176D

✓
Model: BYD Song MAX 2019. Owner reported the airbag warning light stays on. VDS scan retrieved DTC B176D-00 (Left rear seatbelt pretensioner does not exist), history fault. Owner had removed the left rear seat to install floor mats one week prior. Removed the seat and found the pretensioner connector (yellow plug) only half-inserted with the locking tab disengaged. Seat removal pulled the harness, loosening the connector. Reconnected the connector, confirmed the lock engaged, cleared the DTC, and the warning light went out. Road tested 20 km with no recurrence.
BYD DTC AI Analysis

Seat rail crushed wiring harness causing intermittent B176D fault

✓
Vehicle: BYD Qin Pro 2020. Customer reported the airbag warning light illuminated intermittently, particularly after adjusting the left rear seat. The scan tool showed B176D as an intermittent fault. Inspection revealed the pretensioner harness ran too tight beneath the seat rail. Moving the seat forward and rearward pinched the harness against the rail, damaging the insulation and partially breaking the internal copper strands, causing an intermittent open. Repair: Soldered the broken wiring and insulated with heat-shrink tubing, rerouted the harness, added corrugated tubing protection, and ensured clearance throughout the full seat travel. Fault resolved.
BYD DTC AI Analysis

Replaced pretensioner assembly due to internal open circuit

✓
Vehicle: BYD Tang DM 2021. After accident repairs, the airbag warning light remained on. DTC B176D-00. Checked connectors and wiring harness continuity—normal. Pretensioner terminal resistance measured infinite (open circuit). Disassembled pretensioner: internal squib pins fractured from impact. Pretensioners are single-use safety components; internal open circuit cannot be repaired. Replaced left rear seatbelt pretensioner assembly (with retractor). Cleared fault code; system normal. After replacement, perform pretensioner resistance calibration in 'Configuration and Settings' using a diagnostic tool.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.