AU
B176E

DTC B176E indicates the SRS (Supplemental Restraint System) control unit detects an abnormally low-resistance path between the Left Rear Seat Belt Pretensioner drive circuit and the vehicle power supply (+B), indicating a short to power — Atto 3

Safety System

DTC B176E indicates the SRS (Supplemental Restraint System) control unit detects an abnormally low-resistance path between the Left Rear Seat Belt Pretensioner drive circuit and the vehicle power supply (+B), indicating a short to power.

The pretensioner contains a squib controlled by the SRS ECU, with a normal operating resistance of approximately 2.0-3.0 Ω.

If the wiring harness or connector shorts to a 12V power wire, the ECU detects an abnormally high voltage or resistance value, immediately sets this DTC, and enters fail-safe mode.

This fault presents two risks: first, during a collision, circuit protection may prevent the left rear pretensioner from deploying, causing occupant restraint failure; second, the short-circuit current may accidentally trigger the squib, causing the seat belt to retract suddenly and injure the occupant.

Consequently, the SRS system immediately cuts power to this circuit and illuminates the airbag warning lamp, potentially disabling the entire airbag system.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Worn wiring harness or damaged insulation inside the left rear B-pillar contacts vehicle power lines (e.g., constant power or ignition power), causing a short circuit. This commonly results from water exposure or prolonged chafing due to a detached wiring harness retaining clip.
  • 2Left rear seat belt pretensioner connector (usually located under the seat or inside the B-pillar trim): Terminal misalignment, backed-out pins, or water corrosion causing bridging between terminals, especially due to water intrusion after a car wash or during the rainy season.
  • 3During vehicle modifications (such as installing seat heating, floor sound insulation, or a rear entertainment system), technicians accidentally pierced the pretensioner wiring harness or pinched it between the metal frame and the power cable.
  • 4MOSFET or clamping diode breakdown in the SRS control unit internal drive circuit, causing the pretensioner port to continuously output a high level (rare, but requires troubleshooting).
  • 5Internal short circuit in the pretensioner body (short circuit between the squib bridgewire and housing), typically resulting from previous impact deformation or internal moisture ingress.
What To Do
  • 1
    Safety preparation: Switch the vehicle to OFF, disconnect the low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental deployment.
  • 2
    Fault confirmation: Use the VDS2000/BYD dedicated diagnostic tool to read freeze frame data and confirm vehicle status (voltage, temperature, vehicle speed) at the time of the fault. Attempt to clear the fault code. If the code persists, it is a current fault.
  • 3
    Visual inspection: Remove the left rear lower B-pillar trim panel and scuff plate trim. Inspect the pretensioner wiring harness (wrapped in yellow corrugated conduit) for damage, burn marks, or crush deformation. Specifically check for wiring harness interference within the seat slide rail adjustment range.
  • 4
    Circuit measurement: Disconnect the left rear seat belt pretensioner connector (usually marked B176). Use a multimeter to measure the voltage to ground of the two wires on the harness side (ECU side). Normal voltage is 0V or close to 0V (due to the SRS ECU internal pull-down resistor). A 12V reading confirms a short to power.
  • 5
    Sectional isolation: If 12V is present at the harness side, progressively strip the harness sheath along the circuit toward the ECU to locate the contact point with a power wire (e.g., red or orange wires). If the harness is normal, measure the pretensioner resistance (specification: 2.0±0.3Ω). If the resistance is too low, replace the pretensioner.
  • 6
    ECU verification: If both the wiring harness and pretensioner are normal, measure the output voltage at the corresponding SRS ECU pin. If the power supply voltage remains abnormal, this indicates an internal ECU fault. Replace and recode the airbag control module.
  • 7
    Repair verification: After repairing the wiring harness (rewrap using waterproof tape and corrugated conduit, maintaining at least 50mm clearance from the power cable) or replacing the component, reconnect all connectors and the battery. Use the diagnostic tool to perform the "SRS system self-diagnosis" and "configuration test". Confirm DTC B176E does not return and the airbag warning lamp turns off normally.
Real-World Cases
BYD DTC AI Analysis

Song MAX: Left rear seat modification pinched wiring harness, causing short circuit

✓
A 2019 BYD Song MAX with 30,000 km had the airbag warning light on steady. Scanning revealed DTC B176E. The owner reported rear seat heating pads installed at a repair shop one week prior. Removing the left rear B-pillar trim revealed the seatbelt pretensioner harness pinched by the seat heater power cable (red 12V constant) through a metal clamp, with the insulation worn through and copper core exposed. Cut out the damaged section, soldered in an extension, and sealed it with heat-shrink tubing. Rerouted the harness to clear the seat rails and isolated the seat heater power cable. Cleared the fault codes and the SRS system returned to normal.
BYD DTC AI Analysis

BYD Yuan EV: Connector corrosion and short circuit after water ingress

✓
2019 Yuan EV airbag warning light came on after driving in heavy rain. Scanner reported B176E. Inspection found water marks on the left rear sill. Removed the left rear seatbelt pretensioner connector (located below the B-pillar) and found green corrosion and water in the terminals. Resistance between the pretensioner drive terminal and the adjacent constant power terminal measured only 0.5Ω, creating a short. Cleaned the connector with electronic cleaner, blow-dried it, applied conductive anti-corrosion grease, and installed a new waterproof connector housing. Also checked the sunroof drain tubes for blockages to prevent further water ingress. Fault resolved.
BYD DTC AI Analysis

Tang DM wiring harness chafing on sharp body edge

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2021 Tang DM, 80,000 km. Intermittent airbag warning light with fault code B176E. Shake test found the left rear B-pillar harness contacting a sharp burr on the body panel when the vehicle hit bumps. Peeling back the yellow corrugated tubing revealed a deep scratch in the wire insulation that touched chassis ground or adjacent power wires during vibration. Wrapped the damaged area with insulation tape, fitted a rubber sleeve to isolate the sharp edge, and adjusted the harness mounting point for more slack. Road tested 20 km; fault did not return.
BYD DTC AI Analysis

Qin Pro petrol SRS ECU internal driver fault

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2020 Qin petrol variant. After accident repair (left rear quarter panel straightening), replaced the left rear seatbelt assembly, but DTC B176E persisted. Disconnected the pretensioner connector and still measured 12V abnormal voltage on the harness side; the wiring harness was intact with no visible damage. Further disconnected the SRS ECU connector and checked continuity between the pretensioner drive pin and power pin, finding an internal short in the ECU. Root cause: The collision's instantaneous high current damaged the ECU's internal driver chip. Fix: Replaced the airbag control module (matched the vehicle VIN and configuration codes), performed online programming, and cleared the fault.
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.