AU
B174B

This DTC indicates the SRS (Supplemental Restraint System) ECU detects that the igniter circuit resistance for the left rear side airbag (typically located in the left rear seat backrest side or C-pillar trim panel) is below the calibrated threshold (typically < 1 — Qin Plus

Safety System

This DTC indicates the SRS (Supplemental Restraint System) ECU detects that the igniter circuit resistance for the left rear side airbag (typically located in the left rear seat backrest side or C-pillar trim panel) is below the calibrated threshold (typically < 1.5Ω; standard value 2.0 ± 0.3Ω).

Electrically, low resistance usually indicates a parallel resistance path in the circuit.

Possible causes include an inter-turn short circuit in the internal igniter coil, damaged wiring harness insulation shorting to body ground, or conductive contamination between connector terminals.

This fault forces the SRS into a degraded mode.

During a collision, the ECU may disable deployment of the affected airbag due to the circuit anomaly (fail-safe).

Furthermore, if the resistance drops near 0Ω, the system risks inadvertent deployment.

This safety-critical fault requires immediate repair.

The B174B fault code on the Qin Plus indicates the SRS ECU has detected low resistance in the left rear side airbag igniter circuit. Severity is medium, but it is safety-critical because the airbag may be disabled or could deploy unexpectedly if resistance is near zero. Common causes include an internal short in the airbag igniter or damaged wiring shorting to body ground. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Internal short circuit in the left rear side airbag igniter (squib): Aging, moisture ingress, or manufacturing defects in the gas generator ignition coil inside the airbag module cause an inter-turn short circuit, reducing total resistance.
  • 2Harness abrasion causing short to ground: Damage to the harness sheath at the seat frame, slide rail, or hinge allows the igniter harness (usually yellow) to contact vehicle body metal, creating a parallel resistance to ground.
  • 3Connector water ingress or corrosion: An aging left rear door frame seal or driving through water allows moisture to enter the seat side airbag connector. This causes electrolytic corrosion or forms a conductive water film between the terminals, reducing circuit resistance.
  • 4Rear seat modification damage: When non-professionals install seat covers or heating pads, or repair the seat, fixing screws pierce or pinch the wiring harness, damaging the insulation and causing a short circuit.
  • 5SRS ECU sampling circuit fault: A faulty internal A/D converter or sampling resistor in the control unit causes a false low resistance reading (actual resistance is normal, but the detected value is low).
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the low-voltage battery negative terminal, and wait at least 3 minutes to fully discharge the SRS ECU capacitor and prevent accidental airbag deployment.
  • 2
    Fault Confirmation: Connect the VDS or dedicated diagnostic tool, read the fault code, confirm B174B is active, and record the freeze frame data (vehicle speed, temperature, etc., at the time of occurrence).
  • 3
    Physical inspection: Check the airbag symbol area on the side of the left rear seat (door side) for external damage, water stains, or signs of removal; inspect the wiring harness connector under the seat for looseness, backed-out pins, or green corrosion.
  • 4
    Circuit isolation test: Disconnect the SRS ECU connector and the airbag module connector. Use a multimeter to measure the resistance to ground of both terminals on the harness side (should be > 1MΩ) and the continuity resistance between the terminals (should be < 1Ω). Verify the harness insulation is intact.
  • 5
    Airbag module inspection: Use a dedicated airbag resistance meter (or a digital multimeter on the low-resistance setting, verifying equipment safety) to measure the resistance between the two terminals of the airbag module connector. Normal resistance is 2.0±0.3Ω. A reading < 1.5Ω indicates an internal module short circuit.
  • 6
    Fault repair: If the wiring harness has a short circuit, repair the damaged section and protect it with insulating tape and corrugated conduit. If the connector is corroded, clean it with electronic contact cleaner and apply conductive grease. If the airbag module is faulty, replace the left rear side airbag module (replace or transfer the wiring harness simultaneously).
  • 7
    System verification: Restore all connections. After reconnecting power, use the diagnostic tool to clear the fault code. Perform the SRS system self-check (approximately 20 seconds) and confirm B174B does not reappear. Perform a road test and verify the airbag warning light turns off and remains off.
Real-World Cases
BYD DTC AI Analysis

Poor contact at left rear side airbag connector (BYD Qin)

✓
The airbag warning light on my 2020 BYD Qin stayed on. Using a scan tool, I retrieved DTC B174B-00. I found the left rear seat side airbag connector was not fully seated, with a gap of about 1 mm causing unstable terminal contact resistance that sometimes dropped to 0.8 Ω. I disconnected and reconnected the connector, verified the latch engaged fully, and the resistance returned to normal (2.1 Ω). Clearing the DTC fixed the issue.
Original source ↗
BYD DTC AI Analysis

BYD Tang seat rail wear causes wiring harness short circuit

✓
A 2021 BYD Tang had an intermittent airbag warning light while driving. Diagnostics showed DTCs B174B (resistance too low) and B174C (resistance too high) alternating. Removing and inspecting the left rear seat revealed the seat rail rubbing against the wiring harness during fore-aft adjustment, damaging the yellow airbag harness insulation. The copper wires contacted the metal rail, causing an intermittent short to ground. Replaced the damaged harness section, rerouted and secured the harness, and fitted a protective sleeve. The fault was eliminated.
BYD DTC AI Analysis

BYD Song MAX fault after rear seats removed and refitted

✓
A 2019 Song MAX's airbag warning light came on after the owner removed and refitted the left rear seat cover. Diagnostic testing revealed DTC B174B. Inspection found that during removal, the owner had fully unplugged the side airbag connector on the seat backrest. When reconnecting, they misaligned the pins, which deformed the terminals and caused a short circuit. Replaced the airbag harness connector (with terminals) and restored the connections using a dedicated crimping tool. After clearing the fault code, the system returned to normal.
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.