AU
B174C-00

DTC B174C-00 indicates the Airbag Control Unit (ACU) detects the left rear side airbag (typically located on the outboard side of the left rear seat backrest or inside the C-pillar trim panel) igniter resistance exceeds the calibrated threshold (normal range: 1 — Seal U

Safety System

DTC B174C-00 indicates the Airbag Control Unit (ACU) detects the left rear side airbag (typically located on the outboard side of the left rear seat backrest or inside the C-pillar trim panel) igniter resistance exceeds the calibrated threshold (normal range: 1.5-3.0 Ω, typically calibrated around 2.0 Ω).

This SRS continuity monitoring fault indicates a high-resistance condition in the circuit between the ACU and the airbag igniter.

Potential causes include an open circuit, poor contact, or an internal open circuit within the airbag assembly.

This fault prevents the affected airbag from deploying during a collision.

The system illuminates the airbag warning light and disables the associated airbag function.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1The airbag wiring harness connector (usually yellow) under the left rear seat or at the C-pillar is loose, not fully seated, or has poor contact due to a broken locking tab.
  • 2Interference between the seat adjustment mechanism and the airbag wiring harness causes prolonged rubbing against the seat slide rail or frame, damaging the insulation and resulting in a partial wire break or complete open circuit.
  • 3Open circuit or abnormally high resistance in the left rear side airbag assembly internal igniter (squib), common after a vehicle collision (even without deployment) or due to component aging.
  • 4Oxidation, corrosion, or water ingress at plug pins (e.g., from vehicle wading or water entering under the seat during washing), causing increased contact resistance.
  • 5Incorrectly connecting the airbag connector or using an incompatible high-resistance substitute during seat modification or repair (e.g., installing full seat covers or replacing seat upholstery).
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the 12V battery negative terminal, and wait at least 3 minutes to discharge the SRS system capacitor to prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect a diagnostic tool (such as Launch X-431 or BYD VDS), read the DTC to confirm B174C-00 as a current fault, and check the airbag's real-time resistance value in the data stream (usually displays >5Ω or open circuit).
  • 3
    Visual inspection: Remove the left rear seat back trim panel or lower C-pillar trim panel. Inspect the airbag wiring harness connector (yellow marking) for proper seating, an intact locking tab, and any obvious signs of water ingress or oxidation.
  • 4
    Resistance measurement: Disconnect the airbag connector and use a multimeter to measure the resistance across both terminals of the airbag assembly (Note: on some models, connect a 2Ω resistor in series to prevent accidental deployment from static electricity). Normal resistance is 1.5-3.0Ω. If the reading is infinite, the airbag is faulty. If normal, check the wiring harness.
  • 5
    Harness continuity test: Measure harness continuity between the ACU and the airbag connector, and check insulation to ground and power. Inspect the harness for pinching or chafing during seat movement.
  • 6
    Repair procedure: Based on inspection results, clean oxidized connectors (use electrical contact cleaner + conductive grease), repair damaged wiring harnesses (solder + high-temperature insulating tape), or replace the airbag assembly (if replacing, use genuine parts and record the inflator serial number).
  • 7
    System reset: Restore all connections, turn on the power, and clear the fault code using the diagnostic tool. Perform an 'SRS system self-check' or 'configuration write' (required after installing a new airbag). Verify the fault code does not return and the instrument cluster warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Poor contact at left rear airbag connector (intermittent while driving)

✓
The airbag warning light on a 2019 BYD Qin Pro DM illuminated intermittently while driving. Used a VDS2000 scan tool and retrieved DTC B174C-00 (current fault). Removed the left rear seat for inspection and found the airbag harness connector beneath the seat back (yellow 2-pin connector) was not fully latched, with a gap of approximately 2mm. Diagnosed the cause as foot kicking by rear passengers or long-term fore-aft seat adjustment loosening the connector. Reconnected the connector, confirmed the locking tab fully engaged, and secured the harness to the seat frame with cable ties, away from the sliding rails. Cleared the fault code and test drove 50 km; the fault did not return.
Original source ↗
BYD DTC AI Analysis

Seat rail wear caused an open circuit in the wiring harness.

✓
A 2018 BYD Song MAX came in with an airbag warning light that would come on after driving over speed bumps or rough roads, sometimes going out on its own on smooth roads. The scan tool retrieved B174C-00 as a historical/intermittent fault. Removing the left C-pillar trim revealed the airbag wiring harness had been rubbing against the left seat slide rail mounting bracket over a long period. The insulation was worn through, leaving only 2–3 copper strands connected, and vibration would cause a complete break. Repair: cut out the damaged section, soldered a 0.5mm² high-temperature-resistant wire in its place, insulated the splice entirely with heat-shrink tubing, rerouted the harness clear of the seat movement interference point, and added corrugated conduit protection. The fault was completely eliminated.
Original source ↗
BYD DTC AI Analysis

Connector oxidation after water ingress caused high resistance.

✓
A 2017 BYD Qin EV450 developed a constant airbag warning light on startup the day after driving through heavy monsoon rain (water level reached the lower door edges). The scan tool showed code B174C-00. Inspection found damp carpet beneath the left rear seat, visible water staining inside the airbag connector, and green oxidation on the brass pins, causing contact resistance to increase to 12Ω (normal 2Ω). Cleaned the pins thoroughly with anhydrous alcohol and electronic contact cleaner, blew out internal moisture with an air gun, and applied conductive grease to prevent re-oxidation. Also removed the seat to air out the carpet and checked the body drain holes. After the repair, resistance returned to normal; cleared the fault code to resolve.
Original source ↗
BYD DTC AI Analysis

Internal open circuit in airbag module after accident

✓
A 2020 BYD Tang DM had a left-rear side collision, denting the left rear door. After repairs, the airbag warning light stayed on and would not clear. DTC B174C-00 was stored. Checked the wiring harness and connectors and found no visible damage. Disconnected the airbag plug and measured the airbag resistance directly — it showed infinite resistance (open circuit). Diagnosis: the impact broke the internal igniter (squib) or detached the solder ball connection. Fix: Ordered a genuine left rear side airbag assembly (VIN-matched part number). After installing the new airbag, you must use the diagnostic tool to perform ‘SRS ECU Configuration’ and ‘VIN Write’ (required on some models), otherwise the system will report a configuration error. Cleared the fault codes; the system returned to normal.
Original source ↗
BYD DTC AI Analysis

Aftermarket full-coverage seat covers compressed and dislodged the connector

✓
A 2019 BYD Qin Pro displayed an airbag warning light on the instrument panel the day after the owner had full-coverage leather seat covers installed at an automotive accessories market. Diagnostic scan retrieved code B174C-00. Inspection revealed that during installation, the technician completely removed the left rear seat backrest. When reinstalling, the technician did not align the airbag harness connector with its locking slot, instead trapping it between the seat foam and frame. This caused the connector to partially disengage and the pins to deform. Repair: Straightened the deformed pins, reconnected the harness, and confirmed the locking mechanism engaged. Advised the owner to remind technicians to watch out for the airbag harness when modifying seats. Fault resolved.
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.