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B1771A

DTC B1771A indicates the SRS (Supplemental Restraint System) ECU detects the RH rear seatbelt pretensioner circuit resistance is below the calibrated threshold — Atto 3

Safety System

DTC B1771A indicates the SRS (Supplemental Restraint System) ECU detects the RH rear seatbelt pretensioner circuit resistance is below the calibrated threshold. (The standard value is typically 2.0 ± 0.5 Ω; a measured value below 1.2 Ω or near 0 Ω triggers this code).

As a key passive safety system actuator, the pretensioner contains a pyrotechnic combustion chamber and a resistance wire.

Low resistance indicates a short circuit risk (harness chafing to ground, water ingress at the connector, or an internal short from a melted resistance wire).

To prevent accidental deployment or upon determining actuator failure, the SRS ECU illuminates the airbag warning light and may disable the RH rear side airbag and pretensioner deployment.

This disables active tensioning protection for that seat during a collision, increasing occupant injury risk.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Worn seat rails shorted the wiring harness

✓
A 2019 Qin PRO DM with 32,000 km had the airbag warning light on. Diagnostic scanner reported DTC B1771A. Found: wiring harness beneath right rear seat chafed against slide rail mounting bracket, insulation worn through causing positive-to-negative short, resistance measured at 0.8Ω. Repaired harness, installed abrasion-resistant corrugated tubing, rerouted clear of moving parts. Fault resolved.
BYD DTC AI Analysis

Connector corrosion after water ingress caused fault

✓
2018 BYD Qin Pro petrol. Owner reported the airbag warning light stayed on after driving through deep water. Inspection found water staining and corrosion inside the right rear pretensioner connector, with insulation resistance between terminals measuring only 200Ω. Water entered through the door sill trim during wading due to a degraded connector seal. Repair: Cleaned the connector terminals, applied electronic contact cleaner, and fitted a replacement waterproof connector. Fault resolved.
BYD DTC AI Analysis

Connector not locked after accident repair

✓
A Qin PRO DM had its right rear seatbelt assembly replaced after collision repair, but the airbag warning light came on after delivery. DTC B1771A. The pretensioner connector was inserted but the locking tab hadn't clicked into place. Driving vibration caused intermittent contact resistance at the terminals (intermittent low resistance). The fault cleared after reinserting the connector firmly and confirming the locking tab was fully seated.
BYD DTC AI Analysis

Pretensioner internal resistance wire short circuit

✓
2019 BYD Qin Pro, no accidents or water ingress. DTC B1771A appeared suddenly. Disconnected the harness and measured the pretensioner body resistance directly: 0.6Ω. Internal resistance wire short—likely a batch quality defect. Replaced the right rear seatbelt pretensioner assembly (requires replacement with the seatbelt; pretensioners not available separately). Configured the new part and cleared the fault.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.