NO
AU
B173C

DTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4 — Atto 3

Safety System

DTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω).

This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module.

Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module.

This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision.

The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

2019 Song MAX: Right middle row seat airbag connector loose

✓
After driving through water, the SRS warning light stayed on constantly. Retrieved DTC B173C. Inspection found the airbag connector beneath the right middle-row seat (yellow 2-pin plug) was not fully locked, with visible water stains and oxidation inside. Fix: Cleaned the connector terminals with anhydrous alcohol, applied conductive grease, reinserted the plug firmly, and confirmed the locking tab was engaged. Cleared the DTC and resistance returned to 2.4Ω. Fault resolved.
BYD DTC AI Analysis

2021 Tang DM: C-pillar wiring harness wear caused high resistance

✓
Owner reported the SRS warning light occasionally illuminated after driving over bumps. Diagnostic scan revealed intermittent fault code B173C. Removed the right C-pillar trim panel and found the airbag wiring harness sheath damaged where it passes through the body sheet metal, with 3 of 5 internal copper strands fractured. This resulted in normal resistance when measured cold, but resistance fluctuated above 5 Ω during vehicle vibration. Repair: Cut out the damaged harness section and spliced in high-temperature wire of the same specification, sealed with heat shrink tubing, and secured the harness routing to prevent further chafing.
BYD DTC AI Analysis

2019 BYD Yuan EV airbag module internal aging

✓
Accident-repaired vehicle (right side scrape). Replaced the right second-row side airbag, and code B173C set. Measured resistance of the old module at 6.8Ω (damaged) and the new module at 2.2Ω (normal), but the fault persisted after installation. Further inspection showed the Airbag Control Unit (ACU) sustained impact damage in the accident, damaging the internal sampling circuit. Solution: Replaced the SRS control unit and recoded. Fault cleared.
BYD DTC AI Analysis

Qin Pro petrol: Door sill wiring harness connector corrosion

✓
Vehicle in a humid southern region. SRS light stays on with DTC B173C. Inspection found water ingress at the intermediate connector inside the right front sill trim panel (connecting body harness to seat harness) due to aged sealant, causing terminal verdigris. Replaced the entire connector assembly (including terminals and seals), re-crimped the wires, and applied waterproof sealing.
BYD DTC AI Analysis

2020 Song MAX seat modification stretched the wiring harness

✓
One week after fitting aviation seats, the SRS warning light illuminated. Inspection found the modification had excessively stretched the right middle-row side airbag harness, loosening the terminal-to-wire crimp inside the connector. Resistance fluctuated between 3–8 Ω when measured. Repair: Cut off the damaged connector and replaced it with a genuine airbag harness connector. Re-crimped and soldered the connections, ensuring the harness length allows full seat travel.
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.