AU
B164111

This DTC indicates the driver-side seat belt pretensioner ignition circuit shorts to body ground (GND) — Seal U

Safety System

This DTC indicates the driver-side seat belt pretensioner ignition circuit shorts to body ground (GND).

The BYD SRS (Supplemental Restraint System) pretensioner typically uses a pyrotechnic or motor-driven design with an operating resistance of approximately 2.0–3.0 Ω.

When the ACU (Airbag Control Unit) detects the insulation resistance between the driver pretensioner circuit and ground drops below the threshold (typically <100 Ω), it logs a short to ground.

This fault triggers the SRS fail-safe mode: the airbag warning light remains illuminated, the affected pretensioner may fail to deploy during a collision, and the system may stop monitoring other restraint devices, posing a severe safety hazard.

The short circuit may occur at the pretensioner itself, the under-seat wiring harness, the floor wiring harness, or the ACU connector.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Under-seat wiring harness wear: During driver seat fore/aft adjustment, prolonged friction between the pretensioner wiring harness and the seat track or floor metal edge damages the insulation, shorting the copper core to body ground.
  • 2Connector water ingress and corrosion: Water entering the B-pillar or under-seat area during vehicle wading, from a blocked sunroof drain, or during car washing oxidizes the pretensioner connector terminals (usually located under the seat or inside the B-pillar trim). This forms a conductive water film or verdigris between the pins, causing a short to ground.
  • 3Pretensioner internal fault: Internal squib insulation aged and cracked, or poor internal coil insulation during production caused a short circuit between the terminals.
  • 4Wiring harness crush damage: Vehicle modifications (such as installing seat covers or floor mats) or foreign objects (such as coins or metal accessories) entering the seat rails crush the wiring harness, causing insulation damage.
  • 5ACU connector fault: Deformed airbag control unit connector terminals, terminal back-out, or a short circuit between pins causes a false pretensioner circuit short-to-ground detection.
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the 12V battery negative terminal, and wait at least 90 seconds for the SRS capacitor to discharge. Ensure the high-voltage system is in a safe state (applicable to hybrid/pure electric vehicles).
  • 2
    Initial inspection: Visually inspect the pretensioner connector (usually a yellow plug) under the driver's seat and inside the lower B-pillar trim panel for signs of water ingress, corrosion, looseness, or physical damage.
  • 3
    Resistance measurement: Remove the driver's seat (if necessary), disconnect the pretensioner connector, and use a multimeter to measure the pretensioner unit resistance (normal: 2.0-3.0 Ω; if <1 Ω or infinite, the pretensioner is faulty).
  • 4
    Insulation check: Measure the resistance from each of the two pins on the pretensioner harness-side connector to body ground (normal: >1MΩ; if <100Ω, a short to ground exists). Also check for a short circuit between the pins.
  • 5
    Harness inspection: Follow the pretensioner harness routing (from under the seat, along the floor to the centre tunnel) and check the protective sleeve for damage. Focus on wear at the seat slide rail mounting points and carpet retaining strip.
  • 6
    Terminal inspection: Check the corresponding ACU connector terminals (usually located under the center console or inside the center armrest box) for backout, bending, or corrosion. Clean or repair as necessary.
  • 7
    Component replacement: If testing confirms an internal short circuit in the pretensioner, replace the driver seat belt assembly (including the pretensioner). If the wiring harness is damaged, repair or replace the wiring harness. Never use a multimeter to directly measure pretensioner resistance or perform a powered test.
  • 8
    System reset: Reconnect all connectors and the battery, use the VDS2000/VDS3000 diagnostic tool to clear the fault code, perform the SRS system self-check, and confirm B164111 does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Worn seat rails caused wiring harness short to ground.

✓
Vehicle: 2019 BYD Qin Pro DM, 32,000 km. The customer reported the airbag warning light stayed on. Retrieved DTC B164111. Found the seat rail edge had cut through the pretensioner wiring harness sheath beneath the driver's seat; bare copper wire contacted the metal rail, causing a short to ground. The root cause: a detached harness clip let the harness shift and get pinched during seat adjustment. Repair: repaired the damaged wire with heat-shrink tubing, rerouted and secured the harness, added anti-chafe sleeving, and replaced the seat rail felt pad to prevent direct contact. Cleared the DTC, and the system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

After water ingress, connector corrosion caused a short circuit.

✓
Vehicle: E2 EV 2020, mileage 18,000 km. The airbag warning light came on after the vehicle drove through water. Diagnosis found active DTC B164111. Removing the driver seat revealed obvious silt and water stains inside the pretensioner connector (yellow 2-pin plug). Verdigris on the terminal surfaces caused the resistance between the pin and plug housing (ground) to measure only 12 Ω. Root cause: The sunroof drain hose connector had detached, letting rainwater run down the A-pillar into the seat area. Repair: Thoroughly cleaned the connector terminals with electronic cleaner and a precision brush, dried the plug, applied conductive protectant, and repaired the drain hose connector. The pretensioner itself was undamaged, so replacement was not needed.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal short in pretensioner caused circuit failure

✓
Model: Qin EV 2019, 56,000 km. After accident repairs (front-end collision), DTC B164111 set and would not clear. Found the pretensioner had fired without replacement, with an internal squib short circuit. Measured pretensioner resistance at 0.3Ω (well below normal), with continuity to ground. Found the ACU had sent a deployment signal during the accident, but the pretensioner jammed mechanically and did not fully deploy, causing the internal coil to burn out and short circuit. Replaced the driver-side seat belt assembly (including pretensioner), checked the ACU crash records, and reset the SRS. Reminder: During accident repairs, check all restraint devices for prior deployment.
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket seat heater installation pinched the wiring loom.

✓
Model: E3 2020, Mileage: 21,000 km. After the customer installed an aftermarket seat heating pad, the airbag warning light illuminated. DTC B164111 appeared intermittently. Inspection found the installer had deviated from the original wiring route: the added heating pad harness crossed and pressed against the pretensioner wiring harness inside the seat foam, wearing through the insulation and causing contact with the seat frame. Repair: Removed the non-compliant heating pad (non-genuine modification voids warranty). Replaced the damaged pretensioner harness (damage point was on the airbag harness; entire harness replaced for reliability). Refitted the original harness clips.
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]