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 — Seal 6 EV

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 Seal 6 EV 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, in rare cases, deploy unexpectedly. Common causes include an internal short in the airbag squib or damaged wiring shorting to the body. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Left rear side airbag squib internal short circuit: Aging, moisture ingress, or manufacturing defects cause an inter-turn short circuit in the airbag module gas generator igniter coil, reducing total resistance.
  • 2Wiring harness worn and shorted to ground: A damaged harness sheath at the seat frame, slide rail, or hinge allows the igniter wiring harness (usually yellow) to contact the vehicle body metal, creating a parallel resistance to ground.
  • 3Connector water ingress or corrosion: Aging left rear door frame seals or driving through water allows moisture to enter the seat side airbag connector. This causes electrolytic corrosion or creates a conductive water film between the terminals, reducing circuit resistance.
  • 4Rear seat modification damage: Unprofessional installation of seat covers or heating pads, or improper seat repairs, causes fixing screws to 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: Switch the vehicle to OFF, disconnect the negative terminal of the low-voltage battery, and wait at least 3 minutes for the SRS ECU capacitor to discharge fully and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect the VDS or dedicated diagnostic tool. Read the fault codes and confirm B174B is active. Record the freeze frame data (vehicle speed, temperature, etc. at the time of occurrence).
  • 3
    Physical inspection: Inspect the airbag label area on the side of the left rear seat (near the door) 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 good.
  • 5
    Airbag module inspection: Use a dedicated airbag resistance meter (or a digital multimeter on the low-resistance setting, verifying equipment safety first) to measure the resistance between the two terminals of the airbag module connector. The normal value is 2.0±0.3Ω. A measured value < 1.5Ω indicates an internal short circuit in the module.
  • 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 shows corrosion, clean it with electrical contact cleaner and apply conductive grease. If the airbag module fails, replace the left rear side airbag module (replace or transfer the wiring harness simultaneously).
  • 7
    System verification: Reconnect all connections. After connecting power, use the diagnostic tool to clear the fault code. Perform an SRS system self-check (about 20 seconds) and confirm B174B does not return. Perform a road test to 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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.