AU
B1641-00

DTC B1641-00 indicates an abnormal short to body ground in the driver-side seat belt pretensioner igniter circuit — Seal U

Safety System

DTC B1641-00 indicates an abnormal short to body ground in the driver-side seat belt pretensioner igniter circuit.

In the BYD SRS (Supplemental Restraint System) architecture, a low-impedance igniter (normal resistance 2.1–3.0 Ω) triggers the pretensioner.

When the ECU detects circuit resistance below the threshold (typically <0.8 Ω), it determines a short to ground.

This fault causes the following: 1) The SRS system enters fail-safe mode, disabling the driver-side airbag and pretensioner functions; 2) The pretensioner may fail to deploy during a collision, causing occupant restraint failure; 3) Continuous short-circuit current risks unintended pretensioner deployment or SRS ECU driver circuit burnout.

This DTC is a hard fault requiring physical repair before clearing.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Worn harness insulation beneath the seat rail: Frequent driver seat movement causes the pretensioner harness (typically located near the left seat rail) to rub against the metal bracket. Damaged insulation allows the copper core to contact chassis ground.
  • 2Pretensioner connector water ingress and oxidation: During vehicle wading or interior cleaning, a poorly sealed pretensioner connector (usually a yellow plug) located below the B-pillar or under the seat allows an electrolytic conductive path to form between the terminals.
  • 3Internal short circuit in the pretensioner unit: Moisture in the gas generator igniter powder or a manufacturing defect causes igniter coil insulation failure, creating a short circuit to the metal housing.
  • 4Pinched wiring harness due to improper seat removal: During previous seat or carpet repairs, the seat rail mounting bolt crushed the pretensioner wiring harness insulation, or failure to reinstall the harness clip caused contact with a metal body edge.
  • 5SRS ECU internal drive circuit fault: ECU internal pretensioner drive MOSFET breakdown or filter capacitor short circuit causes a false external short circuit detection (disconnect the pretensioner connector and measure harness-side resistance to ground to rule this out).
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use the VDS2000 or Launch PAD5 diagnostic tool to read all DTCs. Check for accompanying fault codes (e.g., B1642 passenger side short circuit) and record the ambient temperature and vehicle status from the freeze frame data.
  • 3
    Visual inspection: Remove the driver seat (leave the wiring harness connected). Check the yellow pretensioner connector under the seat rail and inside the B-pillar trim for looseness, water ingress, or green copper corrosion. Check the wiring harness sleeve for cuts from sharp edges.
  • 4
    Resistance measurement: Disconnect the pretensioner connector and use a digital multimeter to measure the resistance between the pretensioner-side terminals (normal: 2.1-3.0 Ω). Measure the resistance from each terminal to body ground (should be >1 MΩ; if <1 Ω, this confirms an internal short circuit).
  • 5
    Harness continuity test: Measure the resistance to ground of the harness between the ECU and the pretensioner. If a short circuit exists, inspect the harness along its routing for wear points within the seat movement range. Focus on the area behind the seat height adjustment mechanism and the seat rail mounting points.
  • 6
    Component replacement: If the pretensioner unit is shorted, replace the driver seat belt assembly (including the pretensioner). If the wiring harness is shorted, repair the damaged wire and insulate using double-layer heat-shrink tubing. Do not wrap with electrical tape.
  • 7
    System reset: Reconnect all connectors (ensure the yellow connector locking tabs are fully engaged), connect the battery, use the diagnostic tool to clear the DTC, and perform the 'SRS System Configuration' and 'Crash Sensor Calibration' procedures.
  • 8
    Function verification: Perform an SRS system self-check (turn the ignition switch ON and verify the airbag warning lamp turns off after 6 seconds). Use the diagnostic tool to perform an 'Active Test' to verify the pretensioner circuit resistance is within the normal range. Road test the vehicle to confirm the fault does not recur.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Worn seat rails in Qin EV300 causing intermittent short circuit

✓
A 2017 Qin EV300 with 80,000 km displayed an intermittent "Check SRS System" warning on the instrument cluster, with DTC B1641-00 logging intermittently. Inspection found the wiring harness protective sleeve behind the driver's seat rail had worn through on the rail's sharp edge, exposing bare copper cores. On bumpy roads, the damaged harness contacted the chassis, causing intermittent short-to-ground faults. Repair: wrapped the damaged area with insulating tape, fitted corrugated tubing for additional protection, and rerouted the harness to avoid the seat rail movement path. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin 80 pretensioner connector corroded after driving through water

✓
2017 BYD Qin 80. After wading through water approximately 40 cm deep, the airbag warning light remained on. Retrieved DTC B1641-00. Inspection revealed obvious water staining and green copper corrosion inside the driver pretensioner connector (yellow 2-pin plug) located below the B-pillar. Resistance between terminal and ground measured 0.3 Ω (short to ground). Cause: Connector seal deterioration led to seal failure when wading. Replaced the pretensioner wiring harness assembly (connector and harness as one unit). Removed corrosion from the ECU-side connector and applied electronic cleaner spray. Cleared fault codes; system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Replaced Qin EV450 pretensioner assembly due to internal short circuit

✓
2018 Qin EV450: Airbag warning light stays on continuously with DTC B1641-00 that cannot be cleared. Disconnected the pretensioner connector under the seat and measured infinite resistance to ground on the harness side (normal). Measured 0.2Ω between the pretensioner terminals and metal casing, confirming internal short to ground. Disassembled the seatbelt retractor and found moisture inside the pretensioner gas generator. Replaced the genuine driver's seatbelt assembly (part number: SA-5813100), performed SRS system configuration after installation, and resolved the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Wiring harness clip not reset after seat removal and refitting, causing pinched short

✓
Case involves a 2017 BYD Qin 100. The customer reported that immediately after having the seat foam replaced at a repair shop, the airbag warning light illuminated upon starting the vehicle. Technicians found the pretensioner wiring harness trapped between the seat track mounting bolt and the chassis; damaged insulation caused a short to ground. Root cause: failure to reinstall the harness retaining clips during the seat repair allowed the harness to enter the seat slide rail travel path. Technicians replaced the damaged harness section, rerouted the harness per specification, secured the retaining clips, and checked full front-to-rear seat travel to confirm no interference.
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]