UK
AU
B17271A

BYD's diagnostic system assigns two definitions to DTC B17271A depending on the vehicle platform — Atto 3

Safety System

BYD's diagnostic system assigns two definitions to DTC B17271A depending on the vehicle platform.

On early ICE platforms like the Qin PRO, the code indicates the right passenger knee airbag ignition circuit resistance falls below the standard threshold (normal range 1.5–3.0 Ω, measured value <1.0 Ω).

This indicates a hard short in the circuit, an internal short in the airbag module, or damaged wiring insulation, which may prevent normal airbag deployment or cause unintended deployment without a collision.

On newer platforms like e-Platform 3.0 and DM-i, the code indicates a left rear blind spot detection (BSD/BSDA) radar sensor fault.

Causes include hardware damage, CAN communication interruption, a power supply short circuit, or loss of system calibration data.

Both scenarios constitute a safety-related system failure.

The vehicle remains drivable with caution, but safety protection functions operate with limitations.

Repair the vehicle immediately.

5
Cases Logged
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM-i left rear BSD radar failure

✓
After starting the vehicle, the dashboard displayed 'Blind Spot Monitoring System Fault'. When reversing, no warning sounded for obstacles on the left rear side. The diagnostic tool read DTC B17271A (Left Rear Blind Spot Monitoring Radar Signal Abnormality). Removed the rear bumper for inspection and measured the radar connector voltage at 12.4V (normal). Swapped the left and right radar sensors and the fault transferred, confirming the radar unit was faulty. Replaced the genuine left rear BSD radar sensor (EQ-3603100) and performed BSD system calibration, which eliminated the fault.
Original source ↗
BYD DTC AI Analysis

BYD Han EV lane-change assist system false alarm

✓
The BSD warning light illuminated intermittently while driving, especially frequent after rain or washing the car. The left side mirror warning light occasionally stayed on constantly. Scanned DTCs B17271A (left rear radar sensor signal unstable) and U015487. Found a gap with poor sealing between the radar and bumper, and internal oxidation in the connector. Cleaned the terminals, applied conductive grease, re-secured the sensor to ensure proper fit, added waterproof tape, and replaced the radar seal with an improved version. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro DM BSD fault after accident repair

✓
After the left rear collision repair, the instrument cluster displayed a blind spot monitoring fault. The system stored permanent DTC B17271A, which could not be cleared. Diagnostics indicated a 'left rear radar sensor not configured/initialization error' with serial number reading 'FFFFFFFF'. The radar sensor replaced during the accident repair turned out to be an aftermarket unit with an incorrect part number. Replacing it with a genuine left rear BSD radar sensor (EHS-3603100-L) and performing the 'replace radar sensor' configuration and radar alignment calibration restored normal operation.
Original source ↗
BYD DTC AI Analysis

BYD Qin PLUS DM-i BSD system sleep fault

✓
After being parked for a week, the BSD system failed to activate when the vehicle started. The scanner retrieved DTCs B17271A (current/static) and B172C00 (BSD system initialisation failure). Checked left rear radar: power supply normal, but no CAN communication. Measured internal resistance: power supply short to ground (2.3 Ω). The radar's internal voltage regulator module had shorted, causing the auxiliary battery to discharge and triggering the protection circuit. Replaced the left rear blind spot monitoring radar assembly and updated the BSD control module software to Ver 2.3.1. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Seal: Radar signal interference fault

✓
BSD warning light intermittently illuminated at highway speeds (above 80 km/h) but operated normally at low city speeds. Freeze frame data showed an abnormal drop in left rear radar signal-to-noise ratio (SNR) when the fault occurred. Inspection found the left rear fender liner was not properly installed after previous accident repairs, resulting in a radar mounting angle deviation of approximately 5° (standard tolerance: ±3°). Reinstalled the fender liner, adjusted the radar bracket angle, and performed geometric calibration using BSD calibration equipment. The fault no longer reoccurred.
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.