AU
B1771-00

This fault code indicates the right rear seatbelt pretensioner circuit resistance falls below the normal threshold set by the SRS control unit (typically below 1 — Qin Plus

Safety System

This fault code indicates the right rear seatbelt pretensioner circuit resistance falls below the normal threshold set by the SRS control unit (typically below 1.5Ω; standard value is approximately 2.0-3.0Ω).

As a pyrotechnic safety device, the pretensioner contains an igniter and a gas generator.

A low resistance value indicates an abnormally low-resistance path in the circuit.

Potential causes include an internal pretensioner short circuit, a wiring harness short to ground, or connector pins shorted to ground.

This fault forces the SRS system into a degraded mode.

Consequently, the right rear pretensioner may fail to deploy during a collision, and the fault lamp remains illuminated to indicate system failure, severely compromising passive safety protection.

The B1771-00 fault code on the Qin Plus indicates low resistance in the right rear seatbelt pretensioner circuit, putting the SRS system in degraded mode. Severity is medium because the pretensioner may not deploy correctly in a crash. Common causes include a shorted pretensioner igniter or damaged under-seat wiring from seat rail chafing. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Short circuit, moisture ingress, or aging of the right rear seat belt pretensioner internal igniter causes an abnormal drop in internal resistance.
  • 2The seat rail pinches and chafes the under-seat wiring harness, damaging the insulation and causing a short circuit between the power and ground wires.
  • 3Right rear seat belt pretensioner connector (usually located in the C-pillar or under the seat): Bent pins, corrosion from water ingress, or foreign objects causing a short circuit between pins.
  • 4SRS control unit internal sampling circuit fault or abnormal reference voltage causing inaccurate resistance measurement
  • 5Vehicle wading or liquid splashed into the right rear seat area caused a short circuit in the pretensioner connector.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds (3 minutes for some models) to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the right rear C-pillar trim panel and seat. Check the pretensioner wiring harness for signs of abrasion, crushing, or water ingress. Check the connector for oxidation and the pins for deformation.
  • 3
    Resistance measurement: Disconnect the SRS ECU connector and use a digital multimeter to measure the right rear seat pretensioner circuit resistance. Normal resistance is 2.0-3.0 Ω; values below 1.5 Ω indicate low resistance.
  • 4
    Isolation diagnosis: Disconnect the pretensioner connector. Measure the pretensioner resistance (should be close to standard value) and the harness-side resistance to ground (should be greater than 1 MΩ) to determine if the fault is in the pretensioner or the wiring harness.
  • 5
    Component replacement: Upon confirming a faulty pretensioner, replace the entire right rear seat belt assembly (the pretensioner and seat belt are an integrated unit and not serviced separately). Do not repair the igniter tube.
  • 6
    Wiring harness repair: If the wiring harness has a short circuit, repair and rewrap the damaged section. Maintain sufficient clearance from the vehicle body to prevent pinching again.
  • 7
    System reset: Reconnect all connectors and the battery. Use the BYD ED400/ED500 diagnostic tool to clear the fault code. Perform the SRS system self-check. Confirm B1771-00 does not reappear and the resistance data stream returns to normal.
Real-World Cases
BYD DTC AI Analysis

Pretensioner connector corroded and shorted in flood-damaged vehicle

✓
2018 BYD Qin EV450 — airbag warning light constantly on. Scanned B1771-00. Vehicle had prior blocked sunroof drain tube that flooded right rear carpet. Pretensioner connector below C-pillar showed water staining and verdigris. Plug disassembly found micro-short between pins 1-2. Harness side resistance normal; pretensioner body 0.8Ω (abnormal). Drained water, replaced RH rear seatbelt assembly (including pretensioner), repaired connector seal. Fault cleared.
Original source ↗
BYD DTC AI Analysis

Aftermarket seat modification pinched wiring harness, causing short circuit

✓
2017 BYD Qin 100. Owner fitted an aftermarket right rear seat heater and the fault light came on. Inspection found the wiring harness was not secured during installation. Seat rail movement chafed through the pretensioner harness insulation, shorting the two wires. Pretensioner circuit resistance measured 0.3Ω. Replaced the entire harness section to avoid poor connections, rerouted per standard layout, and secured above the seat frame clear of moving parts. Cleared DTCs; resistance returned to 2.4Ω.
BYD DTC AI Analysis

Pretensioner internal squib failed due to aging

✓
High-mileage Qin EV300 (120,000 km) with no accident or water submersion history. Intermittent DTC B1771-00. Pretensioner connector was dry and normal. Disconnected and measured normal harness-side resistance (open circuit), but only 0.5Ω across the pretensioner body pins. Diagnosis: Internal squib chemical aging caused an internal short. Replaced right rear seatbelt assembly. Post-replacement measurement: 2.2Ω; system self-test passed. Pretensioners are single-use; long-term high temperatures accelerate internal chemical changes.
BYD DTC AI Analysis

SRS ECU sampling circuit false positive

✓
2017 BYD Qin 80. After replacing the SRS control unit, DTC B1771-00 appeared, but pretensioner resistance measured 2.1Ω (normal) with no harness shorts. Comparison with the old ECU revealed the new unit had different software with deviated internal resistance calibration parameters. Fix: Upgraded the SRS control unit to the latest software version (V2.3 or higher) and performed coding/configuration. Live data showed normal resistance values and the fault code did not return. False positive; no hardware fault.
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.