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 — Seal U

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 — Seal U
  • 1Oxidation or partial open circuit of the pretensioner internal resistance wire: Long-term use can cause micro-cracks or oxidation at the internal coil weld points, causing the resistance value to drift upwards.
  • 2Poor contact at the yellow SRS connector under the seat: Water ingress, oxidation, or frequent connection and disconnection increases terminal contact resistance at the dedicated airbag connector under the left rear seat (usually located on the inner 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 breaks the copper wire without fully severing it, creating a high-resistance condition.
  • 4Seat modification or seat cover installation compressing the wiring harness: During aftermarket leather seat conversions, seat foam squeezes or retaining clips pinch the pretensioner wiring harness, reducing the conductor cross-sectional area.
  • 5SRS ECU internal sampling circuit fault: In very rare cases, the airbag control module's 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. Check the yellow dedicated 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 connector and the ECU connector. Normal resistance is <1Ω. If >2Ω, check for breaks inside the harness sleeve at the seat slide rail.
  • 4
    Pretensioner unit measurement: Measure resistance directly at the pretensioner connector (standard value: 2.0-3.0 Ω). If the measured value is >4.0 Ω or displays OL (open circuit), confirm a pretensioner unit fault.
  • 5
    Replacement verification: Connect a 2.7Ω dedicated 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 disappears, this confirms a fault in the original pretensioner rather than a wiring issue.
  • 6
    Component replacement: If confirming a pretensioner fault, replace the left rear seat belt assembly (BYD usually supplies pretensioners integrated with the seat belt retractor; they are not available separately). During installation, route the wiring harness correctly and leave sufficient slack to prevent bending.
  • 7
    System calibration: Use the VDS2000 or MDI600 diagnostic tool to clear the fault code, execute the 'SRS System Configuration' and 'Sensor Calibration' procedures, and 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 Seal U 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.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.