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B16F811

DTC B16F811 indicates an unintended electrical connection (short circuit) between body ground and the second circuit of a Supplemental Restraint System (SRS) sensor, typically the low-side drive line or signal return line — Atto 3

Safety System

DTC B16F811 indicates an unintended electrical connection (short circuit) between body ground and the second circuit of a Supplemental Restraint System (SRS) sensor, typically the low-side drive line or signal return line.

In BYD’s SRS architecture, this usually indicates a wiring fault in the seat belt pretensioner igniter, side impact sensor, or seat occupancy recognition sensor.

The SRS control unit detects an abnormally low circuit resistance (approaching 0Ω) and triggers the safety protection mechanism.

This disables airbag and pretensioner deployment to prevent injury from accidental activation.

This constitutes a hard fault, indicating a very high probability of physical wiring damage or an internal component short circuit.

The B16F811 fault code on the Atto 3 indicates a high-severity SRS short circuit to body ground, usually in a seat belt pretensioner, side impact sensor, or seat occupancy sensor circuit. Common causes include a damaged wiring harness chafing against seat rails or trim, or an internal short in the pretensioner igniter. The first step is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Internal short circuit in the seat belt pretensioner squib (component not replaced after a collision or component aging causes the internal bridge wire to melt or short to ground)
  • 2Damaged wiring harness insulation causing a short circuit to vehicle body metal (commonly due to harness chafing at the seat rails, B-pillar trim, or under the carpet).
  • 3Internal driver MOSFET or monitoring circuit fault in the SRS control unit (especially in accident-repaired vehicles with a repaired but unreplaced control unit)
  • 4Connector water ingress, corrosion, or misaligned pins causing a short circuit between the signal and ground wires (common in vehicles driven through water or after washing)
  • 5Tools or screws piercing the wiring harness during repair, causing a hidden short circuit (incorrect routing during collision repair allows the seat rail to pinch the harness)
What To Do
  • 1
    Use a dedicated BYD diagnostic tool (VDS6000 or ED400) to read all DTCs. Check for accompanying DTC B16F511 (first line fault) or other related fault codes. Record freeze frame data to determine the fault location (driver/passenger seat belt pretensioner, left/right crash sensor).
  • 2
    Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 3
    Inspect the target sensor connector (usually located near the seat belt buckle or below the B-pillar) for looseness, corrosion, or water ingress, and visually inspect the wiring harness for obvious damage.
  • 4
    Disconnect the SRS control unit. Use a multimeter to measure the resistance to ground of the second wire from the control unit to the sensor (usually the wire with the smaller terminal number). Normal resistance is greater than 1 MΩ. A reading near 0 Ω confirms a short to ground.
  • 5
    Inspect the wiring harness in sections: Trace the harness routing step by step from the sensor to the control unit. Focus on wear-prone areas such as the seat rail, sill trim panel, and B-pillar. Repair damaged insulation or replace the wiring harness.
  • 6
    If the wiring is normal, measure the resistance of the sensor itself (normal seat belt pretensioner resistance is approximately 2-3Ω; the crash sensor has a specific resistance range). If the resistance is abnormal, replace the sensor assembly.
  • 7
    If the wiring and sensor are normal but the fault persists, the SRS control unit internal drive circuit is faulty. Replace the control unit and perform vehicle configuration (VIN writing and sensor matching).
  • 8
    Reconnect the battery, clear the fault code, and perform the SRS system self-check cycle test. Confirm the fault code does not return and the airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

2021 BYD Qin Pro petrol: Airbag fault after collision repair

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Symptoms: The vehicle had been repaired following a collision. The dashboard displayed an 'airbag fault' warning light. A scan tool retrieved DTCs B16F511 (sensor line 1 short to ground) and B16F811 (sensor line 2 short to ground). The driver and passenger airbags had been replaced, the SRS ECU had been repaired, and both front seat belts had been replaced, but the fault codes could not be cleared. Diagnosis: The technician inspected the relevant wiring and found no issues. According to the DTC definitions, B16F511 and B16F811 indicate a seatbelt sensor or SRS wiring fault. After ruling out external wiring and connector issues, the technician diagnosed an internal fault in the SRS control unit. Resolution: Replace or repair the SRS control unit (airbag ECU), then reprogram it and clear the fault codes.
Original source ↗
BYD DTC AI Analysis

BYD multiple models seat belt pretensioner sensor wiring fault

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Symptoms: Airbag warning light came on. Retrieved DTCs showed B16F811 (sensor line 2 short to earth), with some vehicles also logging B16F511 (sensor line 1 short to earth) simultaneously. Diagnosis: Checked seatbelt pretensioner connector for loose connections or corrosion; measured sensor circuit resistance to earth and confirmed a short; checked SRS control unit power supply and earth connections; investigated whether the vehicle had been in a collision or submerged. Resolution: Repaired or replaced the damaged wiring harness. If the harness tested normal, replaced the seatbelt pretensioner assembly. If both were normal, replaced the SRS airbag control unit.
Original source ↗
BYD DTC AI Analysis

BYD Qin Pro/Song Pro rear seat belt sensor fault (accident vehicle)

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Symptoms After accident repairs, the dash continuously displays airbag system faults. DTC B16F811 cannot be cleared, accompanied by seatbelt pretensioner-related fault codes. Diagnosis Used a factory scan tool to read complete fault data. Inspected the seatbelt pretensioner connectors and found pin retraction or poor contact in some vehicles. Measured pretensioner resistance; normal value is approximately 2–3 Ω. Checked the SRS control unit software version and data integrity. Resolution For repaired airbag control modules, reflash the data or replace the unit. Replace damaged seatbelt pretensioners. Repair any short circuits in the wiring harness, then perform system configuration and calibration.
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.