AU
B174B-00

This DTC indicates the firing circuit resistance of the left rear side airbag (typically integrated into the left rear door C-pillar trim panel or the side of the left rear seat backrest) falls below the SRS control module threshold (normal range 2 — Seal U

Safety System

This DTC indicates the firing circuit resistance of the left rear side airbag (typically integrated into the left rear door C-pillar trim panel or the side of the left rear seat backrest) falls below the SRS control module threshold (normal range 2.0-3.0Ω; fault threshold typically <1.0Ω or near 0Ω).

Low resistance indicates an abnormal low-resistance path in the circuit.

Causes include a short to ground, damaged wiring harness insulation, shorted connector pins, or an internal short in the airbag inflator bridge wire.

This fault forces the SRS system into a degraded mode and illuminates the airbag warning light.

During a collision, the affected airbag may fail to deploy (as the control module detects a short and disables the firing circuit) or, in extreme cases, deploy unintentionally.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Water ingress and oxidation in the left rear sill or C-pillar wiring harness connector: Driving through water, car washing, or poor sealing forms a conductive water film between the connector pins, creating parallel resistance.
  • 2Harness mechanical damage: Improper removal/installation of the rear seat or door sill trim panel causes the seat rail to crush the harness insulation, resulting in a short to body ground.
  • 3Airbag unit internal fault: Short circuit in the igniter bridge wire or moisture in the pyrotechnic charge causes an abnormal drop in resistance.
  • 4Poor connector contact: Backed-out or loose terminal pins increase the effective contact area or cause abnormal bridging (resistance appears low, but contact is abnormal).
  • 5SRS ECU internal detection circuit fault: Control module internal sampling resistor or ADC circuit malfunction causes incorrect resistance reading.
What To Do
  • 1
    Safe power-down: Disconnect the 12V battery negative terminal and wait at least 3-5 minutes for the SRS energy storage capacitor to discharge fully, preventing accidental deployment.
  • 2
    Inspection procedure: Remove the left rear C-pillar trim panel and door sill trim panel. Check the connection status of the white/yellow side airbag connector (usually marked 'Side Airbag').
  • 3
    Initial measurement: Use a high-precision multimeter (with seat belt resistance function) to measure resistance between the airbag connector terminals. Normal resistance is 2-3 Ω. If <1 Ω, disconnect the connector and measure harness-side resistance to ground.
  • 4
    Harness continuity check: Measure harness continuity and insulation from the airbag connector to the SRS ECU (usually under the center console or in the front compartment). Inspect the sill harness bends for chafed insulation and shorts to ground.
  • 5
    Component isolation test: Replace the actual airbag with a 2-3Ω dedicated airbag simulator. If the fault code changes to "resistance too high" or disappears, the airbag unit has a short circuit. Replace the airbag.
  • 6
    Repair procedure: If water ingress is present, clean the connector with electronic contact cleaner, blow dry, and apply conductive grease. If the wiring harness is damaged, repair the insulation using heat-shrink tubing and re-secure the routing.
  • 7
    Replacement and matching: After replacing the faulty airbag or wiring harness, use VDS2000 or Launch X431 to perform 'Airbag System Configuration' (some models require online programming to match the VIN).
  • 8
    Clearance verification: Clear the DTC. Perform an ignition cycle self-check. Verify DTC B174B-00 does not return and the instrument cluster warning light turns off. Read the data stream to confirm the resistance is within 2.0-3.0 Ω.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450 left rear seat side airbag connector water ingress short circuit

✓
Symptoms: After driving through water, the airbag warning light stayed on. VDS detected active fault code B174B-00. Diagnosis: Removed and inspected the left rear sill trim panel. The side airbag harness connector showed obvious water ingress, with green copper corrosion between the pins. Resistance between pins measured only 0.4Ω (short circuit condition). Solution: Cleaned the connector with anhydrous ethanol and blow-dried it. After drying, harness-to-ground insulation tested normal. Reconnected the connector, applied waterproof silicone grease, and cleared the fault code. Circuit resistance returned to 2.4Ω.
Original source ↗
BYD DTC AI Analysis

BYD Qin 100 rear seat wiring harness wear causing low resistance

✓
Symptoms: Dashboard airbag warning light illuminates intermittently, particularly over rough surfaces. Diagnosis: DTC B174B-00 stored as intermittent fault. Removed left C-pillar trim and found side airbag wiring harness chafing against seat mounting bracket. Damaged insulation caused intermittent short to ground; resistance to ground fluctuated between 0.5-5MΩ. Solution: Repaired damaged wiring with heat shrink tubing and insulating tape, re-secured harness to original retaining clip positions, added corrugated tubing protection. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin EV300 airbag module internal short circuit

✓
Symptoms: Airbag warning light stays on continuously; DTC B174B-00 will not clear. Diagnosis: Disconnected the left rear side airbag connector. Resistance across the airbag unit pins measured only 0.6Ω (normal: 2–3Ω), indicating an internal short in the airbag igniter. Harness side resistance to ground measured >10MΩ, normal. Resolution: Replaced the left rear side airbag module (seat backrest removal required). Performed SRS system matching using VDS. After clearing the fault code, resistance reads 2.8Ω, normal.
Original source ↗
BYD DTC AI Analysis

BYD Qin 80: software false alarm and intermittent wiring harness connection

✓
Symptoms: 3-month-old vehicle logged DTC B174B-00. No accident or water submersion history. Diagnosis: Visual inspection of the wiring harness showed no abnormalities. Found slightly backed-out airbag connector pins, causing unstable contact resistance (intermittent low values). The SRS ECU had outdated software. Solution: Re-seated the backed-out pins to ensure full engagement. Updated the SRS control module software to the latest version (optimised resistance sampling algorithm). The fault has not recurred.
Original source ↗
BYD DTC AI Analysis

BYD Qin EV450 seat connector not fully seated after seat removal and refit

✓
Symptom: The owner reported the airbag warning light illuminated after the left rear seat was reupholstered. Diagnosis: Retrieved DTC B174B-00. Inspection revealed the side airbag connector was not fully locked; the internal shorting bar had made unintended contact, causing circuit resistance to drop abnormally to 0.9 ohms. Solution: Reinserted and secured the airbag connector, confirmed the locking tab engaged (audible click), cleared the DTC, and road tested to confirm normal system operation.
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.