AU
B174C

DTC B174C indicates the SRS (Supplemental Restraint System) detects the inflator resistance of the left rear side airbag (usually located inside the left rear C-pillar trim panel or on the side of the left rear seat) exceeds the system-calibrated threshold (typically above 3 — Seal U

Safety System

DTC B174C indicates the SRS (Supplemental Restraint System) detects the inflator resistance of the left rear side airbag (usually located inside the left rear C-pillar trim panel or on the side of the left rear seat) exceeds the system-calibrated threshold (typically above 3.0Ω; normal range is 1.5Ω-3.0Ω).

This fault indicates a high-resistance condition or open circuit in the airbag inflator circuit.

Inflator aging, poor wiring harness contact, or a broken wire can cause this condition.

This fault prevents the airbag from deploying correctly during a side-impact collision and continuously illuminates the dashboard airbag warning light (SRS light).

The system enters fail-safe mode, and some models may limit the seat belt pretensioner function.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose airbag connector at the left rear C-pillar, backed-out pins, or oxidized/corroded terminals causing increased contact resistance.
  • 2Moisture ingress and aging of the igniter charge inside the left rear side airbag module, or an open circuit in the squib coil, resulting in abnormally high resistance.
  • 3Long-term bending and wear of the wiring harness at the rear seat folding mechanism or C-pillar trim panel edge causes internal wire breakage or shielding layer damage.
  • 4Moisture enters the airbag connector during vehicle wading or car washing (especially due to poor sealing at the bottom of the C-pillar), causing slow terminal oxidation.
  • 5Faulty internal sampling resistor or A/D conversion circuit in the SRS control module, causing a false high resistance reading (intermittent fault)
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 3 minutes to discharge the residual charge in the SRS capacitor to prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use the BYD dedicated diagnostic tool (VDS3000) to read the DTC. Confirm B174C is a current fault (Active), not a history fault (History).
  • 3
    Visual inspection: Remove the left rear C-pillar trim panel and check the connection status of the airbag module orange connector. Confirm no backed-out pins, loose connections, or obvious signs of water ingress.
  • 4
    Resistance measurement: Disconnect the airbag connector. Use a digital multimeter (accuracy 0.1 Ω or better) to measure the resistance directly between the airbag-side connector terminals. Standard resistance is 2.0 ± 0.5 Ω. A reading of OL (open circuit) or >5 Ω indicates a damaged airbag unit.
  • 5
    Wiring harness inspection: If airbag resistance is normal, measure end-to-end wiring harness continuity (SRS module to airbag connector). Focus inspection on the wiring harness at the seat hinge and C-pillar pass-through to locate high-resistance points (>1Ω is abnormal).
  • 6
    Simulation test: Connect a dedicated airbag simulator (2Ω resistor) to the circuit in place of the actual airbag. If the fault clears after power-on, the airbag assembly is faulty. If the fault remains, inspect and repair the wiring harness or SRS module.
  • 7
    Repair/Replacement: Replace the faulty airbag or repair the wiring harness (insulate with double-layer heat-shrink tubing after soldering). Rewrap with waterproof tape and ensure the connector locking tab is fully engaged.
  • 8
    System reset: Reinstall all components, connect the battery, and clear the fault codes using the diagnostic tool. Perform the SRS system self-check (Ignition Check) and confirm the warning light turns off and the system has no current faults.
Real-World Cases
BYD DTC AI Analysis

Worn left rear C-pillar wiring harness caused B174C fault in BYD Tang DM

✓
The SRS warning light on the instrument panel stayed on. Scan tool showed active fault code B174C. Removed the left rear C-pillar trim and found the side airbag wiring harness rubbing against the edge of the C-pillar sheet metal hole. The insulation wore through, 90% of the copper strands broke, and only a few strands remained connected, causing intermittent resistance readings. Repair: Cut out the damaged section. Soldered in new 0.5mm² high-temperature fluoroplastic wire (overlap ≥20mm). Insulated with double-layer heat-shrink tubing. Rerouted the harness away from sharp sheet metal edges. Fault cleared.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro Left Rear Side Airbag Connector Oxidation Case

✓
After three years of use, the vehicle developed an intermittent B174C fault with the SRS light illuminating in damp weather. Inspection found green copper corrosion on the terminals inside the left rear seat side airbag connector (beneath the seat backrest), caused by water ingress during car washing that did not dry. Contact resistance between the terminals measured 12Ω. Resolution: Cleaned the terminals with electronic cleaner, applied conductive protective grease, replaced the connector housing with a waterproof type, and re-crimped the terminals. The fault has not recurred.
Original source ↗
BYD DTC AI Analysis

BYD Han EV airbag igniter aging high-resistance fault

✓
Vehicle under collision repair (left rear side impact). After replacing the left rear quarter panel and C-pillar trim, the SRS warning light set DTC B174C. The replacement salvage airbag resistance measured 6.8 Ω (normal: 2.3 Ω). Long-term storage moisture caused chemical degradation inside the igniter. Installed a new left rear side airbag (part no. SA2E-62766-00), performed module configuration programming and system calibration. Resistance returned to normal 2.1 Ω, fault cleared.
Original source ↗
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.