AU
B1774-00

This DTC indicates a short to vehicle power positive (B+) in the right rear seat belt pretensioner ignition circuit — Atto 8

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 Atto 8 indicates a high-severity short to battery power in the right rear seat belt pretensioner ignition circuit. This can stop the pretensioner working correctly in a crash and may create an unintended deployment risk. Common causes include damaged wiring insulation in the right rear C-pillar or water corrosion at the pretensioner connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 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 shorts the coil to the 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.
  • 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-off: Switch 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 the BYD ED400 or VDS diagnostic tool to read the fault code. Confirm B1774-00 is a current (Active) fault rather than a history fault, and record the freeze frame data.
  • 3
    Physical inspection: Remove the right rear C-pillar trim panel and the under-seat cover panel. 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: Use a dedicated SRS probe (to prevent accidental airbag deployment) to measure the pretensioner unit resistance. 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 yellow SRS-specific wiring harness (do not splice with ordinary wire). Maintain a distance of more than 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. 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 Atto 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.