AU
B17271A

BYD's diagnostic system assigns two definitions to DTC B17271A depending on the vehicle platform — Atto 8

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
5
Causes
Likely Causes — Atto 8
  • 1Internal circuit short or breakdown in the left rear BSD radar sensor unit (e.g., damaged voltage regulator module causing a power supply short to ground)
  • 2Water ingress and oxidation at the radar wiring harness connector, loose terminals, or poor contact (common after car washing, driving through water, or in rainy, high-humidity conditions).
  • 3Radar mounting bracket deformed, loose, or misaligned, causing signal interference or calibration failure (common after accident repairs).
  • 4Using a non-genuine or unconfigured aftermarket radar sensor prevents the BSD control module from recognizing the serial number.
  • 5Chafed or damaged body wiring harness insulation causing a power supply short to ground, or an open/short circuit in the CAN network communication harness.
What To Do
  • 1
    Use the VDS2000 diagnostic tool to read all fault codes and freeze frame data. Confirm the B17271A status (current/history/intermittent) and any accompanying fault codes (such as U015487 communication fault).
  • 2
    Visually inspect the left rear bumper radar sensor for physical damage. Check the bracket installation tightness and the fit gap between the bracket and the bumper (gap must be zero).
  • 3
    Disconnect the radar connector and measure the supply voltage (12 V ± 0.5 V), CAN-H (2.5–2.7 V) / CAN-L (2.3–2.5 V), and terminal resistance (approx. 60 Ω).
  • 4
    Perform a swap test on the left and right rear side radar sensors and observe if the fault code transfers with the sensor to determine the condition of the radar unit.
  • 5
    Check wiring harness continuity and insulation. Inspect the inside of the connector for water ingress and oxidation. If necessary, clean with WD-40 and apply conductive grease.
  • 6
    If confirming a faulty radar, replace it with a genuine sensor probe (confirm the part number matches the VIN) and use the diagnostic tool to execute the 'Radar Sensor Replacement' configuration procedure.
  • 7
    Perform BSD system geometric calibration (requires a level surface and dedicated calibration frame). Clear fault codes, then perform a road test to verify (including tests at vehicle speeds >30km/h and >80km/h).
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 8 Fault Codes
B1108For 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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.