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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 — Seal U

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.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Seat belt pretensioner squib internal short circuit (failure to replace 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 panel, or under the carpet).
  • 3Fault in the SRS control unit internal drive MOSFET or monitoring circuit (especially in accident-repaired vehicles with a repaired instead of replaced control unit)
  • 4Water ingress, corrosion, or misaligned pins in the connector causing a short circuit between the signal wire and ground wire (common after vehicle wading or washing).
  • 5A tool or screw punctured the wiring harness during repair, causing a hidden short circuit (incorrect routing during accident repair caused the seat rail to pinch the wiring harness).
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS6000 or ED400) to read all DTCs. Check for accompanying B16F511 (first line fault) or other related fault codes. Record the 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
    Check the target sensor connector (usually located near the seat belt buckle or below the B-pillar) for looseness, corrosion, or water ingress. 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: check the harness routing step by step from the sensor end to the control unit end. Focus on wear-prone areas such as the seat rail, door sill trim panel, and B-pillar. Repair damaged insulation or replace the wiring harness.
  • 6
    If the circuit is normal, measure the sensor resistance (normal seat belt pretensioner resistance is approximately 2-3 Ω; 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 and the fault persists, the SRS control unit internal driver circuit is faulty. Replace the control unit and reconfigure the vehicle (VIN writing and sensor matching).
  • 8
    Reconnect the battery, clear the fault code, and perform the SRS system self-check cycle. Verify the fault code does not return and the airbag warning light turns off.
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 Seal U 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.