AU
B17271A

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

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 Seal U indicates a medium-severity safety system fault, most commonly involving the left rear blind spot detection radar sensor. Likely causes include an internal radar circuit failure or a corroded, loose, or water-damaged wiring connector. The vehicle may still be drivable, but blind spot warnings may be limited or unavailable. Visit an authorised BYD dealer promptly for diagnosis, calibration, and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left rear BSD radar sensor internal circuit short or breakdown (e.g., damaged voltage regulator module causing a power supply short to ground)
  • 2Radar wiring harness connector oxidation due to water ingress, loose terminals, or poor contact (common after car washing, wading, or in rainy, high-humidity environments).
  • 3Deformed, loose, or misaligned radar mounting bracket 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.
  • 5Body wiring harness insulation worn or damaged, 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 damage. Check the bracket mounting tightness and the mating gap with the bumper (there should be no gap).
  • 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 radars. Observe if the fault code transfers with the sensor to determine if the radar unit itself is faulty.
  • 5
    Check wiring harness continuity and insulation. Specifically inspect the connector interior for water ingress and oxidation. If necessary, clean with WD-40 and apply conductive grease.
  • 6
    If the radar is faulty, replace it with a genuine sensor probe (confirm the part number matches the VIN). Use the diagnostic tool to perform the 'Replace Radar Sensor' configuration procedure.
  • 7
    Perform BSD system geometric calibration (requires a level surface and dedicated calibration frame). Clear the fault code, then perform a road test to verify (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 Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.