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 — Atto 3

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 Atto 3 indicates low resistance in the right rear seatbelt pretensioner circuit, putting the SRS system into a 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. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Short circuit, moisture ingress, or aging of the right rear seat belt pretensioner internal igniter, causing an abnormal decrease 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.
  • 3Bent pins, water corrosion, or foreign matter causing a short circuit between pins at the right rear seat belt pretensioner connector (usually located in the C-pillar or under the seat).
  • 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 12V 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. Inspect 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 pretensioner circuit resistance. Normal resistance is 2.0-3.0 Ω; a value below 1.5 Ω indicates low resistance.
  • 4
    Isolation diagnosis: Disconnect the pretensioner connector. Measure the pretensioner resistance (should be close to the 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: If the pretensioner is faulty, replace the entire right rear seat belt assembly (the pretensioner and seat belt are an integrated unit and cannot be replaced separately). Do not repair the squib.
  • 6
    Wiring harness repair: If the wiring harness has a short circuit, repair and rewrap the damaged section. Leave sufficient clearance from the body to prevent further pinching.
  • 7
    System reset: Reconnect all connectors and the battery. Use the BYD ED400/ED500 diagnostic tool to clear the fault code. Perform an SRS system self-test and confirm B1771-00 does not recur 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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.