AU
B1775-00

This DTC indicates an abnormally low-resistance connection (typically <1 kΩ) between the right rear seat belt pretensioner squib circuit and vehicle chassis ground (GND) — Qin Plus

Safety System

This DTC indicates an abnormally low-resistance connection (typically <1 kΩ) between the right rear seat belt pretensioner squib circuit and vehicle chassis ground (GND).

As a pyrotechnic safety device, the pretensioner relies on the SRS ECU to supply a high-current pulse during a collision.

A short to ground causes: 1) abnormal circuit resistance, leading the ECU to register a device fault; 2) potential inadvertent deployment if the short-circuit current reaches the ignition threshold; 3) the SRS system to enter fail-safe mode, disabling the right rear pretensioner and associated seat belt reminder function.

This is a hard fault in the passive safety system that directly affects the integrity of the occupant restraint system.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Wiring harness chafing below the right B-pillar: The pretensioner wiring harness routes through the B-pillar trim to the floor. Long-term fore-and-aft seat adjustment or passenger foot movement wears through the insulation, causing a short circuit to the metal body.
  • 2Connector water ingress and oxidation: Water accumulation on the rear floor (e.g., blocked sunroof drain tube or leaking air conditioning condensate) corrodes the pins of the pretensioner connector (usually located under the seat or at the base of the B-pillar), creating a short-to-ground path.
  • 3Pretensioner unit internal fault: Igniter (squib) internal bridgewire insulation failure or a damp, conductive pyrotechnic charge causes continuity between the terminal and housing.
  • 4Post-accident repair issues: During vehicle collision repair, when repairing B-pillar sheet metal or rerouting the wiring harness, missing harness retaining clips cause the harness to contact sharp edges, or tools scratch the wiring harness during pretensioner removal and installation.
  • 5Manufacturing defect: Wiring harness insulation batch quality issue causing premature aging and cracking at bend points (such as near the seat hinge).
What To Do
  • 1
    Safe power-down: Turn the power switch to OFF, disconnect the negative battery terminal, wait at least 90 seconds (to ensure the SRS capacitor fully discharges), and wear an anti-static wrist strap.
  • 2
    Fault code freeze frame analysis: Connect the VDS or a dedicated diagnostic tool, record the vehicle status (temperature, voltage, mileage) when the fault code occurred, and confirm whether it is an intermittent fault.
  • 3
    Visual inspection: Remove the right rear B-pillar lower trim panel and seat side trim panel. Inspect the pretensioner connector (black/yellow marking) for looseness, water ingress, or discolored pins. Check the wiring harness at the floor trim strip for wear and exposed copper.
  • 4
    Harness-to-ground insulation test: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the harness side (ECU side) and body ground. Normal resistance is >1 MΩ. Measure the voltage to ground. Voltage must be <1 V (to rule out internal ECU short circuit).
  • 5
    Pretensioner unit test: Measure the resistance between the pretensioner terminals (normal: 2.0-4.0 Ω). Measure the resistance between either terminal and the pretensioner metal housing (should be infinite).
  • 6
    Wiring harness repair: If the wiring harness is damaged, repair it using heat-shrink tubing or insulating tape. Install corrugated conduit for protection. Maintain a clearance of at least 20mm from the seat slide rails and body sheet metal. Secure the harness using OEM cable ties.
  • 7
    Component Replacement: If the pretensioner has an internal short circuit, replace the right rear seat belt pretensioner assembly (replace the seat belt assembly simultaneously, as the pretensioner usually integrates into the retractor or mounting base).
  • 8
    System verification: Restore connections, reinstall the trim panel, and connect the battery. Turn the ignition switch ON and confirm the SRS warning lamp turns off after the self-check. Use a diagnostic tool to perform the 'Airbag System Configuration Test' or 'Crash Output Test' (static test mode), clear the fault codes, and perform a road test for verification.
Real-World Cases
BYD DTC AI Analysis

Wiring harness worn by right rear seat rail causing intermittent short circuit

✓
2017 BYD Qin EV300, 80,000 km. Intermittent SRS warning light. Scanner read B1775-00; freeze frame showed rough-road trigger. Inspection revealed the right rear seat rail mounting bolt interfering with the pretensioner wiring harness. Prolonged friction had worn through the insulation, exposing copper wire that contacted the seat frame. Repaired the harness, rerouted the wiring, and installed abrasion-resistant sleeving. Fault resolved.
BYD DTC AI Analysis

Sunroof drain tube detached; water entered and corroded the pretensioner connector.

✓
After driving through water, the SRS warning light stayed on. Retrieved DTC B1775-00. Inspection found the right rear sunroof drain hose connector had detached, letting water run down the A-pillar into the base of the B-pillar. The pretensioner connector pins (located at the floor harness junction) showed severe oxidation and measured only 200 Ω to ground. Cleaned the connector, applied conductive paste, replaced the drain hose connector, and waterproofed the wiring harness. Fault resolved.
BYD DTC AI Analysis

Internal short circuit in pretensioner after accident repair

✓
A BYD Qin 100 repaired following a collision with prior right rear impact. After repairs, DTC B1775-00 was retrieved. Continuity between the pretensioner terminal and housing measured 0.5Ω, indicating the pretensioner internal igniter insulation had been damaged by impact. Replaced the right rear seatbelt pretensioner assembly (including retractor). SRS configuration coding restored normal system operation.
BYD DTC AI Analysis

B-pillar trim improperly installed, crushing wiring harness insulation

✓
The SRS warning light came on the day after window tinting. Customer stated the B-pillar trim was removed during tinting. Inspection found the lower clip on the right rear B-pillar trim misaligned; the panel’s sharp edge crushed the seatbelt pretensioner harness insulation, causing a short to ground. Rerouted and secured the harness, wrapped it with fleece tape to prevent chafing, replaced the damaged clip. Fault cleared.
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.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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.