AU
B110C09

DTC B110C09 indicates a driver-side seat belt pretensioner circuit fault, specifically an open circuit, short to ground, or abnormal resistance (standard resistance 1 — Atto 8

Thermal Management System

DTC B110C09 indicates a driver-side seat belt pretensioner circuit fault, specifically an open circuit, short to ground, or abnormal resistance (standard resistance 1.8-2.5Ω).

This fault relates to the Supplemental Restraint System (SRS).

The Airbag Control Unit (ACU) triggers this code upon detecting driver-side pretensioner circuit voltage or resistance outside the specified threshold.

The pretensioner is a critical safety device operating in conjunction with the airbag.

During a collision, the gas generator tightens the seat belt to eliminate slack between the webbing and the occupant.

This fault forces the airbag system into fail-safe mode and continuously illuminates the instrument panel airbag warning light.

This condition can prevent the pretensioner from deploying during a collision, significantly increasing occupant injury risk.

8
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Internal open circuit or abnormal resistance in the driver-side seat belt pretensioner assembly (e.g., infinite resistance from failing to replace the assembly after accident deployment).
  • 2Loose pretensioner wiring harness connector under the seat, oxidized pins, backed-out pins, or poor contact.
  • 3Fore-and-aft seat movement chafes the wiring harness sleeve between the floor and seat frame, causing an intermittent open circuit or short to ground.
  • 4Burned internal contacts in the seat belt buckle switch causing unstable signal transmission.
  • 5Short circuit to ground, short circuit to power, or electromagnetic interference in the wiring between the airbag control unit and the pretensioner
What To Do
  • 1
    Connect the VDS2000/BYD dedicated diagnostic tool, read the fault code to confirm B110C09, and check the live data stream to verify the driver pretensioner resistance is 1.8-2.5Ω.
  • 2
    Check that the yellow wiring harness plug (pretensioner connector) under the driver's seat is fully seated. Inspect the pins for oxidation or deformation. Clean and apply conductive grease if necessary.
  • 3
    Measure the pretensioner unit resistance: Disconnect the connector and measure the resistance directly across the pretensioner terminals. If the resistance is infinite or >5Ω, replace the driver-side seat belt assembly (including the pretensioner). If normal, check the wiring.
  • 4
    Check the wiring harness routing near the seat rail for insulation wear. Adjust the seat to the fully forward and fully rearward positions. Measure circuit continuity while moving the seat to locate any intermittent open circuits.
  • 5
    If the wiring harness is damaged, repair the wires and install corrugated conduit for protection. Use cable ties to secure the wiring harness to a stationary part of the seat frame. Verify seat adjustment does not pull the harness.
  • 6
    For accident vehicles, check if the pretensioner deployed. After confirming the assembly requires replacement, install a new assembly, connect the diagnostic tool to clear the crash record, and perform airbag system configuration writing and coding matching.
  • 7
    Clear the fault code, perform a system self-check, and verify the airbag warning light turns off after 6 seconds. Conduct a road test and read the fault code again to confirm fault resolution.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro DM - Loose seat belt pretensioner connector

✓
Symptoms: Dashboard airbag warning light stays on after starting. DTC B110C09 (driver side seatbelt pretensioner open circuit). Diagnosis: Inspected wiring harness connector under driver's seat – found loose with slightly oxidised pins. Pretensioner resistance measured 2.1Ω (normal). Determined intermittent open circuit caused by poor connector contact. Repair: Cleaned connector pins and applied conductive grease. Reconnected firmly and secured harness with cable tie near seat rail to prevent pulling when seat moves. Cleared DTC, test drove vehicle – airbag light went out.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song PLUS DM-i - Seatbelt buckle switch internal fault

✓
Symptoms: While driving, the instrument cluster occasionally displayed "Check Airbag System." DTC B110C09 appeared intermittently, easily triggered on rough roads or after adjusting the seat angle. Diagnosis: Connected a diagnostic tool and monitored live data. Found the driver seatbelt buckle switch signal flickering between fastened and unfastened. Removed the buckle assembly and found the internal micro-switch contacts were burnt. Wiring harness voltage measured 12V, within normal range. Fix: Replaced the driver-side seatbelt buckle assembly (part number: SCE-5813100). Recalibrated the seatbelt status, cleared DTCs, and road tested. The signal remained stable.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM accident-repaired vehicle - seatbelt pretensioners deployed but not replaced

✓
Symptom: After front collision repairs, the dashboard continuously displays an airbag fault. DTC B11009C (driver seat belt pretensioner circuit fault). Diagnosis: Reviewed repair records and found the driver pretensioner had deployed (locked) during the frontal impact, but the shop only performed a visual inspection without replacing the unit. Disassembled the component and found the pretensioner internally disconnected with infinite resistance. Solution: Replaced the driver side seat belt assembly (with pretensioner, part number: EM2E-5813100). Connected a diagnostic tool to write the airbag system configuration and match the coding. Cleared the crash records and fault codes, then completed the self-test.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Dolphin - Worn seat wiring harness causes intermittent open circuit

✓
Symptoms: At 8,000 km, the airbag warning light illuminated intermittently. DTC B110C09 set intermittently. The fault occurred mainly when adjusting the seat to full forward or rearward positions, and disappeared when the seat was centred. Diagnosis: Repeated seat adjustment testing revealed a design defect in the wiring harness protective sleeve between the floor pan and seat frame. Long-term friction had damaged the insulation on the pretensioner signal wire (yellow/black), causing a short to ground at specific seat positions. Resolution: Repaired the damaged harness, re-wrapped it with insulation tape, added corrugated conduit, and adjusted the harness routing. Added rubber grommets and harness clips at the seat rail mounting points. Cleared the DTC and performed 20 full-range seat adjustment cycles to confirm the fault was eliminated.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro DM - Loose seat belt pretensioner connector

✓
Symptoms: Dashboard airbag warning light stays on after starting. DTC B110C09 (driver's side seat belt pretensioner open circuit). Diagnosis: Found the wiring harness connector under the driver's seat loose, with slightly oxidised pins. Measured pretensioner resistance at 2.1Ω (normal). Determined that poor connector contact caused an intermittent open circuit. Repair: Cleaned the connector pins and applied conductive grease. Reconnected firmly and secured the harness near the seat rail with a cable tie to prevent pulling when the seat moves. Cleared the DTC and test-drove the vehicle – airbag light went out.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song PLUS DM-i - Seatbelt buckle switch internal fault

✓
Symptoms: The dashboard occasionally displayed "Check Airbag System" while driving. DTC B110C09 appeared intermittently, particularly on rough roads or when adjusting the seat angle. Diagnosis: Connected a scan tool and monitored live data. Found the driver's seat belt buckle switch signal toggling between fastened and unfastened. Removed the buckle assembly and found burnt contacts on the internal micro-switch. Wiring harness voltage was normal at 12V. Fix: Replaced the driver-side seat belt buckle assembly (part number: SCE-5813100). Recalibrated the seat belt status, cleared the DTC, and road tested. The signal remained stable.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM accident-repaired vehicle - seatbelt pretensioners deployed but not replaced

✓
Symptoms: After front collision repairs, the instrument cluster continuously displayed an airbag fault, DTC B110C09 (driver seatbelt pretensioner circuit fault). Diagnosis: Repair history review found the driver pretensioner had deployed (locked) during the frontal impact, but it had only been visually inspected, not replaced. Disassembly revealed the pretensioner was internally disconnected with infinite resistance. Solution: Replaced the driver-side seatbelt assembly (with pretensioner, part number: EM2E-5813100), connected the diagnostic tool to write the airbag system configuration and perform coding match, cleared crash records and fault codes, and completed the self-test.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Dolphin - Worn seat wiring harness causes intermittent open circuit

✓
Symptoms: At 8,000 km, the airbag warning light on the instrument cluster illuminated intermittently. DTC B110C09 appeared intermittently, mainly when adjusting the seat to the full forward or rearward positions, and disappeared when centred. Diagnosis: Repeated seat adjustment testing revealed a design defect in the wiring harness protective sheath between the floor pan and seat frame. Long-term friction damaged the insulation on the pretensioner signal wire (yellow/black), causing a short to ground at specific seat positions. Resolution: Repaired the damaged harness, rewrapped it with insulation tape and added corrugated tubing, and adjusted the harness routing. Added rubber grommets and harness clips at the seat rail mounting points. Cleared the DTC and performed 20 full-range seat adjustment cycles to confirm the fault was resolved.
Other Atto 8 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. Sources: [1]