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 — Qin Plus

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.

The B174C fault code on the Qin Plus indicates the SRS has detected high resistance or an open circuit in the left rear side airbag inflator circuit. This is a medium-severity fault because the airbag may not deploy correctly in a side impact. Common causes include a loose or corroded connector, backed-out pins, or an aged airbag igniter. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Loose airbag connector, backed-out pins, or oxidized/corroded terminals at the left rear C-pillar, 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, causing abnormally high resistance.
  • 3Prolonged 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 damage.
  • 4Moisture seeps into 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.
  • 5SRS control module internal sampling resistor or A/D conversion circuit fault, 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 and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use the BYD dedicated diagnostic tool (VDS3000) to read the DTC and 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. Verify there are no backed-out pins, loose connections, or obvious signs of water ingress.
  • 4
    Resistance measurement: Disconnect the airbag connector. Use a digital multimeter (minimum 0.1 Ω accuracy) to measure the resistance directly between the airbag-side connector terminals. Normal resistance is 2.0 ± 0.5 Ω. If the reading is OL (open circuit) or >5 Ω, the airbag unit is faulty.
  • 5
    Harness inspection: If airbag resistance is normal, measure end-to-end harness continuity (SRS module to airbag connector). Focus inspection on the harness at the seat hinge and C-pillar pass-through hole 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 powering on, the airbag is faulty. If the fault remains, inspect and repair the wiring harness or SRS module.
  • 7
    Repair/Replace: Replace the faulty airbag or repair the wiring harness (insulate with double-layer heat-shrink tubing after soldering). Rewrap with waterproof tape and fully engage the connector locking tab.
  • 8
    System reset: Reinstall all components, connect the battery, clear the fault codes using the diagnostic tool, perform the SRS system self-check (Ignition Check), and verify 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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus overview →
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.