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AU
B171912

DTC B171912 indicates a short to the 12V power supply in the driver-side knee airbag igniter circuit — Atto 3

Safety System

DTC B171912 indicates a short to the 12V power supply in the driver-side knee airbag igniter circuit.

In the BYD SRS system, the normal resistance of the airbag igniter is 2.0 ± 0.3 Ω.

The Airbag Control Unit (ACU) continuously monitors this resistance through a low-current diagnostic circuit.

A "short to power" means the signal wire or return wire in the igniter circuit shorts to the vehicle constant power (B+), causing circuit resistance to rise abnormally (approaching infinity or exhibiting short-circuit characteristics).

This fault is extremely dangerous.

It can cause the airbag to deploy unexpectedly while driving, injuring occupants.

Alternatively, during a collision, the ACU may detect the circuit fault and fail to trigger the airbag, disabling the protection function.

Upon detecting this fault, the ACU immediately illuminates the instrument cluster SRS warning light and locks the airbag system into fail-safe mode.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Qin PRO DM: Knee airbag wiring harness chafed at steering column, causing short circuit

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After wading through water, the airbag warning light illuminated on the dashboard. Retrieved DTC B171912. Inspection found damage to the wiring harness protective sleeve under the driver's knee. Internal copper wires were contacting both the steering column mounting bracket (earth) and nearby power wiring simultaneously, creating a short circuit. Cause: Following water ingress, the wiring harness absorbed water and expanded. Long-term friction against the steering column mounting bracket damaged its insulation, and the moisture also corroded the insulation of the adjacent power wire. Repair: Cut out the damaged section of harness (about 15cm), rerouted the harness away from the steering column movement area, and protected it with corrugated tubing. Fault resolved.
BYD DTC AI Analysis

BYD E2 airbag connector water ingress causing pin short circuit

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After driving during the wet season, the dashboard displayed an airbag warning. The scan tool showed DTC B171912. Removed and inspected the knee airbag connector located beneath the dashboard near the centre console. Found the sealing ring had deteriorated and detached, allowing rainwater to seep in from the floor and pool inside the connector. This created an electrolytic short between the power and signal pins. Solution: Thoroughly cleaned the connector with electronic contact cleaner, blew it dry, replaced the waterproof sealing ring, and applied conductive anti-corrosion grease. The fault has not recurred.
BYD DTC AI Analysis

BYD E3: Full-surround floor mats pinched the wiring harness, causing a short circuit.

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Owner reported the airbag warning light illuminated one week after fitting full-coverage floor mats. Retrieved DTC: left knee airbag short to power. Inspection found the plastic retaining clips used during mat installation were excessively long, penetrating the carpet and piercing the knee airbag wiring harness, causing an internal short between the power wire and the airbag signal wire. Repair: Removed non-compliant clips. Replaced damaged harness section (from main harness branch to connector). Re-routed wiring per specification and secured it with clips away from the floor. Cleared DTCs. System normal.
BYD DTC AI Analysis

Qin EV airbag control unit (ACU) internal drive circuit breakdown

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No collision or modification history. The airbag warning light on the instrument panel suddenly came on and stayed on, logging DTC B171912. Measured the knee airbag harness side—no short to power, harness continuity normal, pins OK. Connected an external airbag simulator; the fault code remained. Found a failed power MOSFET in the left knee airbag driver circuit inside the ACU, causing a short between the output and the internal 12V supply. Replaced the airbag control unit assembly, then performed coding, VIN writing and system calibration using a dedicated diagnostic tool. Fault resolved.
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.