AU
B176F-00

DTC B176F-00 indicates the SRS (Supplemental Restraint System) ECU detects an abnormal electrical connection between the left rear seat belt pretensioner drive circuit and the vehicle power supply (B+) — Atto 3

Safety System

DTC B176F-00 indicates the SRS (Supplemental Restraint System) ECU detects an abnormal electrical connection between the left rear seat belt pretensioner drive circuit and the vehicle power supply (B+).

The pretensioner consists of an igniter and a gas generator, with a normal resistance of 2.0-3.0Ω.

Damaged wiring harness insulation, misaligned connector pins, or an internal pretensioner short circuit cause the ECU to detect an abnormally high circuit voltage (approaching 12V battery voltage) and trigger this DTC.

This fault may result in: 1) Failure of the left rear pretensioner to deploy during a collision, compromising occupant protection. 2) Unintended pretensioner deployment in extreme cases, causing occupant injury. 3) The SRS entering fail-safe mode, disabling all vehicle airbags.

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Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Worn pretensioner wiring harness insulation under the left rear seat or near the B-pillar contacts the body power wire (constant or ignition power), causing a short circuit.
  • 2Water ingress, oxidation, or bent pins at the pretensioner connector (usually located under the seat or inside the B-pillar trim), causing a short circuit between the power and signal terminals.
  • 3Insulation failure in the left rear seat belt pretensioner igniter coil, causing an internal short to power.
  • 4During vehicle modifications (such as installing seat heaters or ambient lighting), the technician accidentally connected the pretensioner wiring harness in parallel with the power wire or pierced the harness insulation.
  • 5SRS ECU internal driver circuit fault (MOSFET breakdown) causing false short-circuit detection (low probability)
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the left rear seat and lower B-pillar trim panel. Inspect the pretensioner wiring harness (usually in a yellow sleeve) for wear, crushing, or burn marks. Focus on the harness within the seat slide rail movement range.
  • 3
    Connector inspection: Disconnect the pretensioner connector and inspect the pins for corrosion, water ingress, or deformation. Measure the voltage to ground at the harness terminal on the connector side to check for an abnormal 12V voltage.
  • 4
    Component test: Use a digital multimeter to measure the pretensioner body resistance (must remain stable between 2.0-3.0Ω). If the resistance measures 0Ω or infinite, or shows continuity to the power supply, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If the wiring harness is damaged, repair it using high-temperature insulating tape (or replace the entire wiring harness). Maintain a distance of at least 10cm from the power cable to prevent electromagnetic interference.
  • 6
    System reset: Reconnect all connectors and the battery. Use VDS2000 or the BYD dedicated diagnostic tool to clear the fault code. Perform 'SRS system self-check' and 'configuration write' (if installing a new component).
  • 7
    Function verification: Perform an ignition cycle test to confirm the fault code does not reappear. Verify the airbag warning light turns off after the self-check. Finally, perform a road test.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450 left rear seat rail chafed through wiring harness causing short circuit

✓
2018 Qin EV450, 42,000 km. Constant airbag warning light. DTC B176F-00. The pretensioner harness under the left rear seat had chafed against the slide rail mounting bolt edge during fore/aft adjustment, wearing through the insulation. The copper core contacted the seat heater power wire (red, 12V constant). Replaced the entire yellow harness from the floor harness to the pretensioner (PN 4C-5823456) and added retaining clips to prevent contact with metal edges. Cleared the DTC; system returned to normal.
BYD DTC AI Analysis

Qin 100 rear seat water ingress caused connector short circuit

✓
2017 BYD Qin 100. After heavy rain, water pooled in the left rear footwell and wasn't cleaned up. DTC B176F-00 set intermittently. Tore down the B-pillar and found the 2-pin pre-tensioner connector underneath had taken on water. Electrolytic corrosion between the pins produced verdigris, dropping insulation resistance between the power and pre-tensioner drive pins below 200 Ω (normal: infinite). Fix: Cleaned the connector with electronic cleaner, blew it dry, applied conductive grease, replaced the waterproof seal, and cleared the door drain holes to stop it happening again.
BYD DTC AI Analysis

Incorrect wiring of aftermarket seat heater caused fault

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The owner had a heating pad installed on the left rear seat at a third-party workshop. The technician incorrectly spliced the heating pad power feed into the pretensioner wiring harness, mistaking the yellow wiring for the seat power supply. This caused the pretensioner circuit to connect directly to 12V power. The vehicle immediately set code B176F-00 at power-up, and the code could not be cleared. Repair actions: Removed the unauthorised modification, replaced the damaged pretensioner (internal igniter likely damaged by high-voltage impact), restored the factory wiring layout, and explained to the owner that the SRS system prohibits unauthorised modifications.
BYD DTC AI Analysis

Pretensioner internal coil aged and short-circuited

✓
A Qin EV300 with 80,000 km and no accident history suddenly set DTC B176F-00. Harness visual inspection revealed no damage. With the connector disconnected, the harness side showed no short to power, but the pretensioner terminals measured 0.5Ω to case. Internal igniter coil insulation had degraded and shorted. Replaced the left rear seatbelt assembly (includes pretensioner, PN 4C-6912345). Fault resolved. Note: Pretensioners are single-use components; even without deployment, internal materials can degrade after long-term use.
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.