AU
B174C1B

This fault code indicates the Airbag Control Module (ACM) detects the squib circuit resistance of the left rear side airbag (typically integrated into the left rear seat backrest side or C-pillar trim panel) exceeds the calibrated upper limit — Seal 6 EV

Safety System

This fault code indicates the Airbag Control Module (ACM) detects the squib circuit resistance of the left rear side airbag (typically integrated into the left rear seat backrest side or C-pillar trim panel) exceeds the calibrated upper limit.

Normal airbag squib resistance ranges from 1.5Ω to 3.0Ω.

The ACM logs a 'high resistance' fault when it detects the value continuously exceeding the threshold (typically above 4.5Ω).

This active safety system functional fault means the airbag may deploy abnormally, deploy late, or fail to deploy completely during a side-impact collision, disabling side protection for the left rear passenger.

An abnormal drop in squib circuit conductivity causes this fault.

Increased contact resistance, a partial open circuit, or an aging internal squib spiral coil can trigger this condition.

The B174C1B fault code on the Seal 6 EV indicates high resistance in the left rear side airbag squib circuit, which may cause delayed, abnormal, or failed airbag deployment in a side impact. This is a medium-severity safety fault. Common causes include a loose, corroded, or water-damaged connector under the left rear seat or B-pillar, or chafed wiring near the seat rail. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1The airbag wiring harness connector under the left rear seat or at the B-pillar is loose, oxidized, or corroded by water ingress, increasing contact resistance.
  • 2Frequent seat adjustment causes the wiring harness to chafe at the slide rail mounting point and partially break the copper strands (intermittent contact), creating a high-resistance condition.
  • 3Aging, open circuit, or manufacturing defect of the internal igniter in the left rear side airbag module
  • 4SRS control module (ACM) internal detection circuit fault or backed-out terminal pin, causing a false abnormal resistance reading.
  • 5Previous vehicle wading, high-humidity environments, or improper car washing caused oxidation inside the airbag wiring harness connector, forming an oxide layer.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS energy storage capacitor. Use the diagnostic tool to read the freeze frame data and confirm B174C1B is a current DTC, not a history fault.
  • 2
    Visual inspection: Remove the left rear seat assembly (or lower C-pillar trim panel). Locate the left rear side airbag wiring harness connector (usually a yellow plug). Check for looseness, signs of water ingress, green oxidation, or backed-out terminals. Check the wiring harness sleeve at the seat slide rail for damage.
  • 3
    Resistance measurement: Use a dedicated SRS low-current resistance tester (do not use a standard multimeter). Disconnect the airbag connector and measure the resistance between the two igniter terminals. The standard value is 2.0±0.3Ω. If the measured value exceeds 4.5Ω or is infinite, diagnose the airbag unit as faulty.
  • 4
    Harness continuity check: Use a multimeter in buzzer mode to measure harness continuity between the airbag connector and the SRS control module. Specifically inspect the continuity and insulation of the transition harness under the seat. Measure the resistance between both ends of the harness; it must be less than 1Ω.
  • 5
    Substitution verification: Connect a 2.0Ω dedicated airbag simulation resistor to the original wiring harness connector. Clear the DTC, power on, and run a self-check. If the DTC changes to 'B174C-00' (resistance too low) or disappears, the fault is in the airbag unit. If the DTC remains, check the wiring harness or ACM.
  • 6
    Repair procedure: Clean oxidized connectors with electrical contact cleaner and apply conductive grease; repair damaged wiring harnesses by soldering and insulate with dual-layer heat-shrink tubing; if the airbag unit is faulty, replace the left rear side airbag assembly (install new retaining bolts).
  • 7
    System verification: Restore all connections and connect the battery. Use the diagnostic tool to perform the 'SRS system self-check' and 'crash output test'. Confirm B174C1B does not return and the instrument panel SRS warning light turns off normally after the self-check.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM seat rail wiring harness wear caused resistance drift

✓
A 2019 Qin Pro DM with 32,000 km had an intermittent SRS warning light on the instrument cluster. Retrieved DTC B174C1B (current). Inspection found that when adjusting the left rear seat, the harness beneath the seat chafed against the metal edge of the seat rail, causing one copper wire to break 90% of the way through without fully severing, creating a high-resistance condition (measured at 6.8Ω). Repair: Cut and re-soldered the damaged wire, insulated it with double-layer heat shrink tubing, and repositioned the harness retaining clips to prevent further chafing. Cleared the fault code and monitored for one week; no recurrence.
BYD DTC AI Analysis

Water-wading vehicle airbag connector oxidation fault

✓
2018 BYD Qin Pro (petrol). Water entered the cabin, reaching seat height. Afterwards, the vehicle logged DTC B174C1B. Removed the left rear seat and found water stains and green copper corrosion inside the airbag harness connector (located on the left side of the seat frame). Surface oxidation on the pins increased contact resistance to 5.2 Ω. Repair: cleaned the male and female terminals thoroughly with precision electronic cleaner, lightly sanded the pins with fine sandpaper until metallic luster was restored, applied special conductive grease, and reconnected. Inspected other airbag harnesses on the same side—no abnormalities found. Reassembled the components and the fault was eliminated.
BYD DTC AI Analysis

Open circuit inside left rear side airbag

✓
2019 Qin Pro DM collision repair. After replacing the left rear side airbag, DTC B174C1B set. Measured the new airbag resistance: infinite. Diagnosed an open in the internal igniter, possibly due to improper transport or storage. Installed a second airbag assembly; resistance 2.1 Ω, normal. However, the fault returned after installation. Further inspection found the airbag control module connector had been jarred loose in the accident, causing pin 14 (left rear side airbag circuit) to back out. Repaired the pin; fault resolved.
BYD DTC AI Analysis

False fault - ACM internal detection circuit malfunction

✓
A 2018 BYD Qin Pro had DTC B174C1B, but the left rear side airbag resistance measured 2.0Ω (normal) and the wiring harness showed good continuity with no damage. Tried replacing the airbag assembly; the fault remained. Checked the ACM diagnostic pulse waveform with an oscilloscope and found it abnormal. Diagnosed an internal constant current source circuit fault in the SRS control module. Replaced the SRS control module (requires VIN matching and coding configuration), after which the fault code cleared and the system returned to normal.
BYD DTC AI Analysis

Poor connector contact in low-temperature conditions

✓
A 2019 Qin Pro DM owner in a cold northern region reported the SRS warning light coming on during winter morning startups and going out after driving for some time. The vehicle stored historical fault code B174C1B. Inspection found no oxidation on the airbag connector under the left rear seat, but at low temperatures (-15°C), thermal expansion and contraction created a micro-gap between the plug and socket, increasing contact resistance to 4.2Ω (threshold). Repair: Adjusted the connector locking tab to ensure full engagement, applied conductive grease rated for low-temperature performance to the pin surfaces, and added wiring harness securing points to relieve stress. Follow-up low-temperature testing confirmed the fault did not return.
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.