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B1780

This fault code indicates the SRS (Supplemental Restraint System) control module failed to detect the normal load resistance (typically 2 — Atto 3

Safety System

This fault code indicates the SRS (Supplemental Restraint System) control module failed to detect the normal load resistance (typically 2.0-3.0Ω) in the Second Row Right Seatbelt Pretensioner circuit during the self-check, registering an open circuit.

The pretensioner is a key actuator in the passive safety system.

It contains an igniter and a gas generator.

During a frontal or side collision, it detonates to produce high-pressure gas, instantly retracting the seatbelt to firmly secure the occupant in the seat and prevent secondary impact injuries.

This fault completely disables the second-row right seatbelt pretensioner.

The SRS enters degraded mode and continuously illuminates the instrument cluster airbag warning light (SRS light).

Some models may also disable the coordinated deployment of the corresponding side airbag, significantly reducing the occupant protection level in a crash.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Song MAX pretensioner connector loose after seat removal and refitting

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Symptoms: After routine maintenance, the SRS warning light on the dashboard stayed on constantly. VDS scan retrieved current DTC B1780. Diagnosis: The right middle-row seat slides frequently due to third-row entry function use. The yellow pretensioner connector locking tab under the seat had not fully engaged, leaving approximately 0.5mm of clearance; driving vibration caused poor contact. Pretensioner body resistance measured 2.3Ω (normal), but the connector terminals showed slight oxidation. Resolution: Cleaned the connector terminals with dedicated terminal cleaner, reseated the plug until the locking tab clicked, and secured the wiring harness to the stationary section of the seat frame using cable ties to prevent interference with the slide rails. Fault resolved.
BYD DTC AI Analysis

Tang DM seatbelt pretensioner internal squib open circuit

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Symptoms: Vehicle in normal use with no collision history. SRS light stays on after startup. Diagnostic tool reads B1780; code will not clear. Diagnosis: Disconnected battery negative terminal. Unplugged right middle-row pretensioner connector. Measured pretensioner pins directly: infinite resistance (open). Removed seatbelt assembly (pretensioner integrated with retractor). Found internal igniter solder joint fractured from metal fatigue due to long-term micro-vibration. Solution: Replaced right middle-row seatbelt assembly (includes pretensioner). Part number per EPC: BYD-58191-XXXX. Performed "Seat Belt Pretensioner Resistance Learning" with diagnostic tool. Cleared fault codes. System returned to normal.
BYD DTC AI Analysis

Seat bracket chafed Yuan EV floor wiring harness

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Symptoms: SRS light flashes intermittently on rough roads; normal on smooth surfaces. DTC B1780 stored as intermittent fault. Diagnosis: Checked connections under the seat—all secure. Measured pretensioner resistance while sliding the seat back and forth; the reading jumped from 2.1Ω to open circuit. Pulled back the carpet and inspected the floor harness: the front seat mounting bracket’s sharp inner edge had worn through the wiring. Vibration caused the two conductors to intermittently disconnect. Fix: Repaired the damaged conductors. Re-wrapped with waterproof tape and corrugated tubing. Rerouted the harness to avoid the seat slide path. Added a rubber sleeve to the sharp bracket edge. Fault eliminated.
BYD DTC AI Analysis

Qin Pro EV: Aftermarket seat cover installation left connector unplugged

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Symptom: Customer reported the SRS warning light lit after having leather seat covers fitted at the dealership. Diagnosis: During the seat cover installation, the technician removed the right middle row seat but failed to reconnect the pretensioner connector. The connector hung loose beneath the seat with the locking mechanism damaged. Resolution: Replaced the damaged SRS connector (with integral shorting bar), re-crimped the terminals and applied waterproofing. Reconnected the harness, cleared the fault codes with a scan tool, performed an SRS cyclic test, and confirmed all airbags and pretensioners functioned normally.
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.