AU
B175C

DTC B175C indicates the airbag control unit (SRS ECU) detects that the igniter (squib) resistance for the right rear side airbag (typically located in the right rear seat backrest side or C-pillar area) exceeds the upper normal threshold — Atto 8

Safety System

DTC B175C indicates the airbag control unit (SRS ECU) detects that the igniter (squib) resistance for the right rear side airbag (typically located in the right rear seat backrest side or C-pillar area) exceeds the upper normal threshold.

The SRS system continuously monitors each airbag igniter's resistance via a low-current circuit; the normal range is typically 1.5-3.0 ohms.

If the resistance remains above approximately 3.5-4.5 ohms (specific thresholds vary by model), the system flags a 'resistance too high' condition.

This fault indicates a high-resistance state in the airbag circuit.

Possible causes include poor connector contact, a partially broken wiring harness, igniter degradation, or a faulty ECU internal sampling circuit.

Safety Impact: Insufficient current may prevent this airbag from deploying during a collision, or the system may trigger a safety strategy disabling the entire airbag system, degrading occupant protection.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Loose right rear side airbag connector, water ingress causing oxidation, or backed-out terminals (commonly affects connectors under the seat or inside the C-pillar trim panel, where frequent seat adjustment or damp environments increase contact resistance).
  • 2Internal aging or a partial open circuit within the airbag igniter causes abnormally high internal resistance (common in older vehicles or vehicles exposed to high temperatures).
  • 3Worn wiring harness or broken strands, especially in the under-seat harness. Long-term bending and friction partially break the copper strands, reducing the effective conductive cross-sectional area (the seat harness protective sleeve design on some BYD models has a wear risk).
  • 4Internal detection circuit fault in the SRS control unit, such as an abnormal sampling resistor or A/D converter, causing a false high resistance reading.
  • 5Wiring harness damage during modification or repair, such as accidentally damaging the airbag harness when installing seat covers or modifying the audio system, or improper repair after an accident.
What To Do
  • 1
    Use the VDS diagnostic tool to read the DTC freeze-frame data, confirm the environmental conditions (temperature, voltage) when the fault occurred, and check for history DTCs or related DTCs (such as sub-code B175C-00).
  • 2
    Perform the safe power-down procedure: Disconnect the battery negative terminal and wait at least 3 minutes for the SRS capacitor to fully discharge to prevent accidental airbag deployment.
  • 3
    Locate the right rear side airbag module (Yuan/Song MAX: usually on the outer side of the right rear seat backrest; Tang/Qin: may be on the C-pillar side). Remove the relevant interior trim panels to expose the connector.
  • 4
    Visually inspect the connector for looseness, water ingress, oxidation, or terminal deformation. Use the dedicated airbag tester (or an equivalent alternative method from the workshop manual) to measure the igniter circuit resistance. Never measure directly using a multimeter resistance setting, as this may deploy the airbag.
  • 5
    Check wiring harness continuity. Inspect the wires inside the protective sleeve under the seat for wear or broken strands. Use a multimeter to measure the end-to-end harness resistance. Resistance must be less than 1 ohm, and insulation resistance must be greater than 1 MΩ.
  • 6
    If the measured resistance is abnormal, replace the right rear side airbag assembly (including the igniter) or repair the wiring harness fault. If the wiring harness is normal but resistance remains high, replace the SRS control unit.
  • 7
    Reconnect all components and restore power. Clear the fault code using VDS. Run the 'SRS System Self-check' or 'Crash Detection Sensor Calibration' procedure. Verify B175C does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Oxidized connector under right rear seat of Song MAX caused high resistance.

✓
A 2019 Song MAX with 42,000 km illuminated the airbag warning light. Retrieved DTC B175C. Removed the right rear seat and found obvious oxidation inside the yellow side airbag wiring harness connector. Terminal surface oxidation increased contact resistance to 5.2 ohms. Cleaned the terminals with electronic contact cleaner, applied conductive grease, and reconnected the connector. Resistance measured 2.1 ohms. Cleared the DTC; fault resolved. A rear passenger spilled a drink that seeped into the connector, causing the oxidation.
BYD DTC AI Analysis

BYD Tang DM: Frequent seat adjustment caused internal wiring harness wire strands to break

✓
2021 BYD Tang DM. Right rear side airbag intermittently setting DTC B175C. The side airbag igniter wiring harness routes through the seat frame on this model. Frequent forward/backward adjustment of the right rear seat (this owner uses it for child safety seat installation) broke the internal copper strands at the bend point while the outer sheath remained intact. Resistance measured intermittent, fluctuating between 3–8 ohms. Replaced the harness assembly, rerouted to add slack, and fitted an abrasion protection sleeve. Fault resolved.
BYD DTC AI Analysis

BYD Yuan EV Airbag Igniter Body Replacement Case – Aging

✓
2019 BYD Yuan EV. B175C appeared after 5 years and could not be cleared. With the harness disconnected, resistance from the SRS ECU to the airbag measured normal at 0.3 ohms. Direct measurement across the airbag assembly terminals showed 4.8 ohms, outside the 1.5–3.0 ohm range. Fault: internal igniter degradation. Replaced the right rear side airbag assembly; resistance returned to 2.3 ohms and the system self-test passed. On older vehicles, replace the airbag assembly directly.
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.