AU
B1774-00

This DTC indicates a short to vehicle power positive (B+) in the right rear seat belt pretensioner ignition circuit — Seal U

Safety System

This DTC indicates a short to vehicle power positive (B+) in the right rear seat belt pretensioner ignition circuit.

In the BYD SRS (Supplemental Restraint System) architecture, the seat belt pretensioner is a pyrotechnic actuator.

Its normal operating resistance is 2.0-3.0 Ω, and the circuit must remain isolated from the vehicle power supply.

When the SRS ECU detects an abnormal resistance drop (near 0 Ω) or a short to power in this circuit, it triggers DTC B1774-00 and enters fail-safe mode.

This fault prevents the right rear seat belt pretensioner from tensioning normally during a collision.

In extreme cases, short-circuit current may cause the pretensioner to deploy unintentionally, presenting a severe safety hazard.

The system illuminates the airbag warning lamp and may disable the entire right-side airbag system.

The B1774-00 fault code on the Seal U indicates a high-severity short to battery positive in the right rear seat belt pretensioner ignition circuit. This can stop the pretensioner working in a crash and may create an unintended deployment risk. Common causes include damaged wiring in the right rear C-pillar or water/corrosion in the pretensioner connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Worn insulation on the pretensioner wiring harness inside the right rear C-pillar trim panel contacts the body power wiring harness (such as constant +B or IGN power), causing a short circuit.
  • 2Poor sealing of the seat belt pretensioner connector (usually located under the seat or at the C-pillar) allows water ingress, causing electrolytic corrosion and a short circuit between terminals.
  • 3Damaged igniter insulation inside the pretensioner body causes continuity between the coil and housing (short to vehicle power).
  • 4During rear seat removal and installation, interior trim panel repair, or seat cover installation, a retaining clip crushes and damages the wiring harness, exposing the copper wire and causing contact with the power wire.
  • 5An internal fault in the SRS ECU driver circuit causes an abnormally high-level output to the pretensioner circuit, resulting in a false short-to-power detection.
What To Do
  • 1
    Safe power-down: Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds (to fully discharge the SRS capacitor and prevent accidental deployment).
  • 2
    Fault confirmation: Use a BYD ED400 or VDS diagnostic tool to read the fault code. Confirm B1774-00 is a current (Active) fault, not a history fault. Record the freeze frame data.
  • 3
    Physical inspection: Remove the right rear C-pillar interior trim panel and the cover beneath the seat. Visually inspect the pretensioner wiring harness (wrapped in yellow corrugated conduit) for damage, scorching, or crush marks.
  • 4
    Connector diagnosis: Disconnect the pretensioner 2-pin connector. Use a multimeter to measure continuity between the harness-side terminal and body ground, and to the +B power supply, to locate the short circuit.
  • 5
    Component isolation test: Use a dedicated SRS probe (to prevent accidental airbag deployment) to measure pretensioner body resistance. Standard value: 2.0-3.0 Ω. If resistance is <1 Ω or infinite, replace the pretensioner assembly.
  • 6
    Wiring harness repair: If the wiring harness is damaged, replace the entire yellow dedicated SRS wiring harness (do not splice with ordinary wire). Maintain a clearance of at least 50 mm from the power wiring harness.
  • 7
    Insulation verification: After repair, use a megohmmeter to measure the insulation resistance between the pretensioner circuit and the power supply. The resistance must be >10MΩ.
  • 8
    System reset: Reconnect all connectors, turn on the power, clear the fault code, perform the SRS system self-check cycle (cycle the ignition switch ON-OFF 3 times), and confirm the fault code does not reappear.
Real-World Cases
BYD DTC AI Analysis

C-pillar trim panel retaining clip crushed through wiring harness, causing short circuit

✓
A 2018 Qin EV450’s airbag warning light suddenly illuminated while driving. The scan tool retrieved DTC B1774-00. Removing the right rear C-pillar trim revealed a retaining clip installed off-centre had pierced the yellow SRS wiring harness sheath. The exposed copper wire contacted the clip (which connects to battery positive via the body), creating a short to power. Replaced the damaged SRS harness section (approx. 30 cm), reinstalled the C-pillar trim clip correctly, and reinforced the wiring protection with electrical tape. Fault cleared.
BYD DTC AI Analysis

Water entered during rear window tinting, corroding connectors and causing a short circuit.

✓
2017 BYD Qin 100 airbag warning light stayed on after rain. Found standing water in the right rear seatbelt pretensioner connector (under the seat) with green corrosion on the terminals. Traced to previous window tinting work that let water into the C-pillar; the connector seal had also aged. Repair: Cleaned the terminals with electronic contact cleaner and a specialized brush, replaced the waterproof seal, tested the pretensioner (passed), cleared the fault codes. System back to normal.
BYD DTC AI Analysis

Power supply line incorrectly connected during aftermarket heated rear seat installation

✓
A 2017 Qin EV300 developed a B1774-00 DTC after rear seat heaters were installed. Technicians found the installer had incorrectly tapped the heater power into the SRS pretensioner wiring, leaving the pretensioner circuit continuously powered with excessive current. We removed the unauthorized wiring, replaced the heat-damaged pretensioner harness (insulation melted), recoded the SRS ECU, and restored factory wiring. Fault cleared.
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.