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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.

The B17271A fault code on the Atto 3 indicates a medium-severity safety system fault, usually involving the left rear blind spot detection radar sensor. Common causes include an internal radar sensor short or breakdown, or water ingress, corrosion, loose terminals, or poor contact in the radar wiring connector. The vehicle may still drive, but safety assistance may be limited. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Internal circuit short or breakdown in the left rear BSD radar sensor (e.g., damaged voltage regulator module causing power supply short to ground)
  • 2Water ingress, oxidation, loose terminals, or poor contact at the radar wiring harness connector (common after car washes, wading, or exposure to rainy, high-humidity environments)
  • 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 body wiring harness insulation causing a power supply short to ground, or open/short circuit in the CAN network communication harness.
What To Do
  • 1
    Use the VDS2000 diagnostic tool to read the complete fault codes and freeze frame data. Confirm the B17271A status (current/history/intermittent) and accompanying fault codes (e.g., U015487 communication fault).
  • 2
    Visually inspect the left rear bumper radar sensor for physical damage. Check the bracket mounting tightness and the fitment gap with the bumper (there must be no gap).
  • 3
    Disconnect the radar connector and measure the supply voltage (12V ± 0.5V), CAN-H (2.5-2.7V) / CAN-L (2.3-2.5V), and terminating resistance (approx. 60Ω).
  • 4
    Swap the left and right rear side radar sensors. Observe if the fault code follows the sensor to determine if the radar unit is faulty.
  • 5
    Check the wiring harness for continuity and insulation, specifically inspecting the inside of the connector for water ingress and oxidation. If necessary, clean with WD-40 and apply conductive grease.
  • 6
    If confirming the radar is faulty, replace it with a genuine sensor (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 the fault codes and perform a road test to verify the repair (including testing at vehicle speeds >30 km/h and >80 km/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 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 overview →
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.