NO
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 — Seal U

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.

4
Cases Logged
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 Seal U 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.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.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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.