AU
B16511B

This DTC indicates the SRS (Supplemental Restraint System) detects the front passenger-side seat belt pretensioner squib resistance exceeds the system calibration threshold (typically >4Ω or near open circuit) — Seal U

Safety System

This DTC indicates the SRS (Supplemental Restraint System) detects the front passenger-side seat belt pretensioner squib resistance exceeds the system calibration threshold (typically >4Ω or near open circuit).

The pretensioner is a critical component of the airbag system.

During a collision, it fires a pyrotechnic charge to rapidly tighten the seat belt and eliminate slack between the occupant and the belt.

High resistance indicates the ECU may fail to supply sufficient current to deploy the pretensioner during a collision.

This deprives the front passenger of pretensioner protection and increases injury risk.

This is a hard fault.

The SRS warning lamp remains illuminated and the system enters degraded mode.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose pretensioner connector plug, oxidized terminal pins, or corrosion from water ingress causing increased contact resistance (common after vehicle wading or washing)
  • 2Aging, moisture, or a partial open circuit in the seat belt pretensioner internal igniter increases internal resistance (the pretensioner is a single-use component; resistance drifts after aging).
  • 3A hidden open circuit, partially broken copper core, or poor crimp connection in the wiring causes abnormally high circuit resistance (common in accident-repaired vehicles or pinched wiring harnesses).
  • 4Frequent seat adjustment wears through or breaks the wiring harness under the front passenger seat (applicable to models with seat-integrated pretensioners; some Qin PRO configurations use this design).
  • 5SRS control unit (ACU) internal detection circuit fault or abnormal sampling resistor (less common; confirm after ruling out external wiring).
What To Do
  • 1
    Safe power isolation: Turn off the ignition switch, disconnect the battery negative terminal and wrap it with insulating tape. Wait at least 90 seconds for the SRS capacitor to fully discharge, preventing accidental airbag deployment.
  • 2
    Visual inspection: Inspect the dedicated yellow pretensioner connector below the front passenger-side B-pillar (or on the outer side of the seat) for looseness, backed-out terminals, oxidation, or water ingress. Check the wiring harness sleeve for damage.
  • 3
    Resistance measurement: Disconnect the pretensioner connector. Use a digital multimeter to measure the resistance between the two pretensioner terminals (standard value: 2.0-3.0Ω). If the measured value is >4Ω or displays OL (open circuit), the pretensioner itself is faulty.
  • 4
    Wiring harness continuity test: Measure circuit continuity between the pretensioner connector and the corresponding SRS control unit pin (must be <1Ω), and measure harness insulation to ground (must be >1MΩ) to check for high resistance or short circuits.
  • 5
    Fault isolation: If the pretensioner resistance is normal, inspect the connector terminals for spreading or bending. Use the special tool to restore terminal contact pressure. Replace the connector or repair the wiring harness if necessary.
  • 6
    Component replacement: After confirming a pretensioner fault, replace the front passenger seat belt pretensioner assembly (Qin PRO models usually require replacing the complete seat belt retractor assembly). Never directly measure pretensioner resistance with a multimeter for longer than the specified time (to prevent accidental deployment).
  • 7
    System reset and verification: Reconnect the battery. Use the BYD dedicated diagnostic tool (ED400/ED600) to clear the fault code. Perform 'SRS system self-diagnosis' and 'pretensioner resistance learning' (if supported). Confirm B16511B does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Oxidized B-pillar connector caused high contact resistance.

✓
A 2019 Qin PRO DM with 80,000 km showed a constant airbag warning light. Read DTC B16511B. Inspection found significant green corrosion inside the yellow pretensioner connector below the passenger-side B-pillar, with inadequate terminal contact pressure. Cleaned the connector using a specialised contact cleaner, applied conductive grease, adjusted the terminal opening, and reconnected. Measured resistance returned to 2.3 Ω. Cleared the fault codes; issue resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat adjustment chafes pretensioner harness, causing high resistance

✓
2018 Qin PRO petrol, with electrically adjustable passenger seat. Owner reported the airbag warning light illuminated intermittently, particularly after adjusting the seat. Inspection found the pretensioner wiring harness sheath under the seat rail had cracked, leaving only three copper strands connected and causing high resistance. Repaired the harness, added an abrasion-resistant sheath, and secured the harness routing to prevent interference with the seat frame. Fault fully resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

After accident repair, resistance drift from pretensioner internal aging

✓
An accident-repaired Qin PRO DM had its front bumper and passenger airbag replaced, but DTC B16511B could not be cleared. Inspection found the seatbelt pretensioner had deployed during the accident but was not replaced during the repair—the shop only cleared the DTCs. After deployment, the pretensioner’s internal structure had changed, and its resistance had risen to 6.8Ω. Replacing the passenger seatbelt assembly (including the pretensioner) with a new unit returned resistance to normal and resolved the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Connector corroded by water ingress after wading.

✓
After driving through standing water, the airbag warning light illuminated. The diagnostic tool showed DTC B16511B. I found water staining in the front passenger footwell and B-pillar area. Water had accumulated inside the pretensioner connector, causing the pins to oxidise and produce high resistance. I cleaned the connector with anhydrous ethanol, dried it with compressed air, applied insulating silicone grease, and checked that the drain holes were clear. The resistance values returned to normal after the repair. I cleared the fault code and it has not returned.
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. Sources: [1]