AU
B1774-00

This DTC indicates a short to vehicle power positive (B+) in the right rear seat belt pretensioner ignition circuit — Seal 6 EV

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 6 EV indicates a high-severity short to vehicle power in the right rear seat belt pretensioner ignition circuit. This can stop the pretensioner working in a crash and may affect the airbag system. Common causes include damaged wiring insulation 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.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 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.
  • 2A poorly sealed 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/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 drive circuit causes an abnormally high-level output to the pretensioner circuit, resulting in a false detection of a short to power.
What To Do
  • 1
    Safe power-off: 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 the BYD ED400 or VDS diagnostic tool to read the fault code. Confirm B1774-00 is a current fault (Active), not a history fault. Record the freeze frame data.
  • 3
    Physical inspection: Remove the right rear C-pillar interior trim panel and the trim 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 terminals and body ground, and between the terminals and the +B power supply, to locate the short circuit.
  • 5
    Component isolation test: Use the dedicated SRS probe (to prevent accidental airbag deployment) to measure the pretensioner body resistance. Standard value: 2.0-3.0Ω. If the resistance is <1Ω or infinite, replace the pretensioner assembly.
  • 6
    Wiring harness repair: If the wiring harness is damaged, replace the entire dedicated yellow SRS wiring harness section (do not splice with ordinary wire). Maintain at least 50mm clearance 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. 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 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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.