AU
B176C1B

DTC B176C1B indicates the airbag control module (SRS ECU) detects the left rear seat belt pretensioner circuit resistance exceeds the calibrated upper limit (typically >5 — Atto 3

Safety System

DTC B176C1B indicates the airbag control module (SRS ECU) detects the left rear seat belt pretensioner circuit resistance exceeds the calibrated upper limit (typically >5.0Ω, normal range 2.0-3.5Ω).

The pretensioner is a pyrotechnic safety device containing an internal resistance wire and propellant.

The ECU determines its readiness by continuously monitoring the circuit current.

Excessive resistance usually indicates a high-resistance connection in the circuit, a partial open circuit, or aging of the internal pretensioner coil.

This condition can prevent the pretensioner from deploying correctly during a collision, seriously reducing the effectiveness of the occupant restraint system.

This fault is a hard fault in the passive safety system.

It generally illuminates the instrument cluster SRS warning light continuously and triggers a warning chime on some models.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Pretensioner internal resistance wire oxidation or partial open circuit: Long-term use may cause micro-cracks or oxidation at the pretensioner internal coil weld points, increasing the resistance value.
  • 2Poor contact at the yellow SRS connector under the seat: Water ingress, oxidation, or frequent disconnection and reconnection cause increased terminal contact resistance at the dedicated airbag connector under the left rear seat (usually located on the inboard side of the seat rail).
  • 3Seat slide rail wiring harness fatigue fracture: On Qin PRO models, folding or adjusting the left rear seat fore/aft repeatedly bends the wiring harness at the slide rail. This partially fractures the copper wire without completely severing it, creating a high-resistance condition.
  • 4Seat modification or seat cover installation compressing the wiring harness: During aftermarket leather seat conversions, seat foam or retaining clips squeeze or damage the pretensioner wiring harness, reducing the conductor cross-sectional area.
  • 5SRS ECU internal sampling circuit fault: In very rare cases, the airbag control module A/D conversion circuit or internal sampling resistor malfunctions, causing a false high resistance reading.
What To Do
  • 1
    Safety preparation: Turn off the ignition, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the left rear seat cushion. Inspect the dedicated yellow SRS connector under the seat (usually marked AIRBAG) for looseness, water ingress, or green oxidation. If necessary, use a special probe to check terminal tension.
  • 3
    Harness continuity test: Disconnect the SRS ECU and pretensioner connectors. Use a multimeter to measure the harness resistance between the pretensioner and ECU connectors. Normal resistance is <1 Ω. If the resistance is >2 Ω, check for a break inside the harness sleeve at the seat slide rail.
  • 4
    Pretensioner unit measurement: Measure resistance directly at the pretensioner connector (standard value: 2.0-3.0Ω). If the measured value is >4.0Ω or shows OL (open circuit), this confirms a pretensioner unit fault.
  • 5
    Replacement verification: Connect a dedicated 2.7Ω substitute resistor into the circuit, connect the battery, and clear the fault code. If the fault code changes to 'B176C-00 Resistance too low' or does not return, this confirms the original pretensioner is faulty, not the wiring.
  • 6
    Component replacement: If confirming a faulty pretensioner, replace the left rear seat belt assembly (BYD usually supplies pretensioners integrated with the seat belt retractor and does not provide them separately). During installation, route the wiring harness correctly and leave sufficient slack to prevent bending.
  • 7
    System Calibration: Clear the fault code using the VDS2000 or MDI600 diagnostic tool. Perform the 'SRS System Configuration' and 'Sensor Calibration' procedures. Finally, perform an ignition cycle test to confirm the warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Worn seat rail wiring harness causes intermittent warning on Qin Pro DM

✓
A 2018 Qin PRO DM with 60,000 km displayed an intermittent "Check SRS System" warning on the instrument cluster, logging DTC B176C1B. Inspection revealed damaged wiring harness sheathing at the left rear seat rail; one of two internal wires was fractured 90% through, held by only a few remaining copper strands. The owner frequently folded the rear seats to carry loads, bending the harness repeatedly at the rail corner and causing metal fatigue. Repaired the harness, added abrasion-resistant corrugated tubing, and relocated the mounting point to increase the bend radius. Fault resolved.
BYD DTC AI Analysis

Oxidized connector on water-damaged vehicle caused resistance drift

✓
2019 Qin Pro petrol. Water entered beneath the left rear seat due to a blocked sunroof drain, triggering DTC B176C1B. Disassembly revealed water stains and verdigris inside the SRS connector below the seat; terminal oxidation pushed contact resistance to 8.5Ω. Repair: Cleaned the terminals with electronic contact cleaner and precision electrical lubricant, restoring normal resistance at 2.3Ω. Cleared the drain tube, applied waterproof silicone grease at the connector, and verified the seal remained intact to prevent further water ingress.
BYD DTC AI Analysis

Aftermarket leather seats pinched the wiring harness, causing high resistance.

✓
One week after having leather seats fitted at an out-of-town trim shop, the SRS warning light illuminated. A scan revealed DTC B176C1B. Inspection found the left rear pretensioner harness wrapped too tightly in the seat foam and pinched at the seat frame edge, deforming the harness. The internal conductors remained intact, but the reduced effective cross-section increased resistance to 4.8Ω. Repair: Rerouted the harness to avoid sharp seat frame edges, wrapped it in foam to prevent direct compression, and confirmed resistance had returned to 2.1Ω. Fault cleared.
BYD DTC AI Analysis

High-mileage case of internal pretensioner coil degradation

✓
A commercial Qin PRO DM with 280,000 km had a persistent B176C1B code that would not clear. Wiring checked out normal; direct measurement at the pretensioner plug showed 6.2Ω (well outside specification). Dismantling the seat belt retractor revealed micro-cracks in the pretensioner’s internal resistor wire solder joints from long-term vibration, increasing contact resistance. Replaced the left rear seat belt assembly (part number: XXXXX-XXXXX). Post-installation resistance measured 2.2Ω and the system self-test passed.
BYD DTC AI Analysis

Loose connector causing intermittent fault

✓
The SRS warning light occasionally illuminated on rough roads but worked normally on smooth surfaces. DTC B176C1B showed 'History/Intermittent' status. Inspection found the left rear SRS connector fully seated, but the internal locking tab had fractured. Vehicle movement made the connector shift slightly, causing poor contact. Special probe testing showed terminal retention force below 1N. Replaced the wiring harness terminal (part number: XXXX-XXXX) and repaired the connector housing, ensuring the locking mechanism remained intact. Road testing confirmed the fault did not return.
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.