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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 — Atto 3

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
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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.