AU
B1774-00

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

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 Qin Plus indicates a short to battery positive in the right rear seat belt pretensioner ignition circuit. This is a high-severity SRS fault that can prevent the pretensioner from working in a crash and may create a safety risk. Common causes include damaged wiring insulation in the right rear C-pillar area or water-corroded pretensioner connectors. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Worn insulation on the pretensioner wiring harness inside the right rear C-pillar trim panel contacts the body power wiring harness (such as constant power +B or IGN power), causing a short circuit.
  • 2Poor sealing of the seat belt pretensioner connector (usually located under the seat or C-pillar) allows water ingress, causing electrolytic corrosion and a short circuit between terminals.
  • 3Damaged insulation on the igniter inside the pretensioner body causes continuity between the coil and housing (short to vehicle power).
  • 4During rear seat removal/installation, interior trim panel repair, or seat cover installation, a retaining clip crushes and damages the wiring harness, exposing copper wire that contacts the power wire.
  • 5SRS ECU internal drive circuit fault 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 switch, 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 trim panel under 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 from the harness-side terminals to body ground and to the +B power supply to locate the short circuit.
  • 5
    Component isolation test: Measure the pretensioner body resistance using a dedicated SRS probe (to prevent accidental airbag deployment). Standard value: 2.0-3.0 Ω. If the resistance is <1 Ω or infinite, replace the pretensioner assembly.
  • 6
    Wiring harness repair: If the wiring harness is damaged, replace the entire dedicated yellow SRS wiring harness (do not splice with ordinary wire). Maintain a clearance of at least 50mm 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-test cycle (cycle the ignition switch ON-OFF 3 times), and verify the fault code does not return.
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 Qin Plus 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.