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
5
Causes
Likely Causes — Seal U
  • 1Short circuit, moisture ingress, or aging in the right rear seat belt pretensioner internal igniter, causing 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.
  • 3Bent pins, corrosion from water ingress, or foreign matter in the right rear pretensioner connector (usually located in the C-pillar or under the seat) 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 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 wear, crushing, or water ingress. Inspect 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. A reading 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 1MΩ) to determine whether the fault is in the pretensioner or the wiring harness.
  • 5
    Component replacement: If confirming a pretensioner fault, replace the complete right rear seat belt assembly (the pretensioner and seat belt are an integrated unit; do not replace them separately). Do not repair the squib.
  • 6
    Wiring harness repair: If the wiring harness has a short circuit, repair and rewrap the damaged section. Ensure sufficient clearance from the vehicle body to prevent further pinching.
  • 7
    System reset: Reconnect all connectors and the battery. Clear the fault code using the BYD ED400/ED500 diagnostic tool. Perform an SRS system self-check and verify B1771-00 does not return 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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.