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B178F-00

DTC B178F-00 indicates an abnormally low resistance connection (typically <1Ω) between the front passenger dual-stage frontal airbag Stage 2 squib circuit and body ground (GND) — Atto 3

Safety System

DTC B178F-00 indicates an abnormally low resistance connection (typically <1Ω) between the front passenger dual-stage frontal airbag Stage 2 squib circuit and body ground (GND).

The dual-stage airbag system achieves staged inflation via two independent igniters: the first stage triggers a small amount of gas, and the second stage triggers delayed supplemental inflation based on collision severity.

A short to ground causes: 1) The SRS control module to detect a circuit anomaly, illuminate the airbag warning lamp, and disable the system. 2) Unintended airbag deployment in extreme cases. 3) The second stage to fail to deploy normally during an actual collision, reducing protection effectiveness.

This fault involves a high-voltage ignition circuit and is a safety-critical fault.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450: Seat Adjustment Causing Wiring Harness Wear Case

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2018 Qin EV450 with 80,000 km: owner reported the airbag warning light stays on. Retrieved DTC B178F-00. Inspection found the SRS wiring harness beneath the front passenger seat rubbing against the seat rails during fore-aft adjustment. The insulation wore through, shorting the copper wires to ground. Repair: Repaired the harness, protected it with corrugated tubing, and repositioned the harness retaining clips to prevent interference throughout the full seat travel range. Fault resolved.
BYD DTC AI Analysis

Qin 100 airbag connector corrosion after water ingress

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2017 BYD Qin 100 developed a B178F-00 fault code after driving through heavy floodwater. Disassembly revealed deterioration of the airbag connector seal below the centre console; water ingress caused short circuits between pins and to earth. Cleaned the connector and treated it with electronic contact cleaner; insulation resistance returned to normal. Replace the connector seal and apply conductive grease for protection.
BYD DTC AI Analysis

Wiring harness unsecured after accident repair caused short circuit

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A Qin 80 with a previous front-end collision set DTC B178F-00 one month after the dealership replaced the passenger airbag. The technician had not secured the airbag harness properly; the dashboard metal bracket pinched it, causing a short to ground. Rerouted the harness and fitted a protective sleeve. Cleared the fault. After accident repairs, verify harness routing and securing.
BYD DTC AI Analysis

SRS Control Module False Positive Case

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2017 Qin EV300 intermittently threw DTC B178F-00, sometimes returning days after clearing. Airbag harness and assembly resistance measured normal (2.1Ω, insulation to ground >10MΩ). Diagnosed as SRS control module internal monitoring circuit fault. Replaced the airbag control module and recoded/matched; fault has not returned.
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.