AU
B1780

This fault code indicates the SRS (Supplemental Restraint System) control module failed to detect the normal load resistance (typically 2 — Seal 6 EV

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.

The B1780 fault code on the Seal 6 EV indicates an open circuit in the second-row right seatbelt pretensioner, disabling that pretensioner and turning on the SRS warning light. Severity is medium because crash protection for that seat may be reduced. Common causes include a loose yellow under-seat connector or a failed pretensioner igniter. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1The pretensioner wiring harness connector under the right middle-row seat (usually a yellow plug) is loose, has a backed-out terminal, or has poor contact. This commonly occurs after seat removal and installation during maintenance, frequent use of the third-row access function, or incomplete reconnection after carpet cleaning.
  • 2Open circuit or abnormal resistance (resistance >5Ω or <1Ω) in the internal igniter of the seat belt pretensioner body. Likely causes include extended pretensioner service life, internal moisture ingress, or previous external impact.
  • 3Long-term mechanical friction on the floor wiring harness within the seat slide rail adjustment range damages the insulation and breaks the wires, or seat mounting bolts crush the wiring harness during installation, causing a hidden open circuit.
  • 4Driving through water or a blocked sunroof drain causes water to accumulate on the floor. This water enters and oxidizes the pretensioner connector (located at the lowest point under the seat), triggering an intermittent high-resistance or open-circuit fault.
  • 5During non-professional modifications (such as installing aviation seats, wooden flooring, or 360 soft trim), installers accidentally cut or short-circuit the pretensioner wiring harness, or perform work without using the dedicated shorting plug.
What To Do
  • 1
    Safe power-off and discharge: Turn the ignition switch to the OFF position, disconnect the negative battery cable, and wait at least 3 minutes (5 minutes for some models) to completely discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Physical connection check: Move the right middle-row seat to the fully forward and fully rearward positions. Verify the yellow SRS dedicated connector under the seat (usually equipped with a double-locking mechanism) is fully seated. Inspect the terminals for green copper corrosion, backed-out pins, or cracks in the connector housing.
  • 3
    Static resistance measurement: Reconnect the battery (for measurement only) and use a digital multimeter to measure the resistance between the pretensioner connector terminals. The standard value is 2.0 ± 0.5 Ω (refer to the specific model repair manual). An infinity (OL) reading confirms an open circuit inside the pretensioner or wiring; a 0 Ω reading indicates a possible short circuit.
  • 4
    Harness continuity and insulation test: Disconnect the SRS control module connector. Measure harness continuity between the pretensioner connector and the corresponding ECU pins (<1 Ω). Measure insulation resistance from the harness to body ground and between the wires (>1 MΩ). Inspect the harness sleeve at the seat slide rail bend.
  • 5
    Component replacement verification: If the circuit tests normal, replace the pretensioner assembly with a known good unit (Note: Do not use an analogue multimeter or apply power to measure pretensioner resistance; use only a digital multimeter for a quick spot check), or swap the left and right pretensioners to confirm if the fault moves with the component.
  • 6
    System configuration and reset: After repairing the fault, connect the diagnostic tool (VDS2000 or Launch X431). Access the SRS system and perform 'Coding Configuration' (for some models, write specific resistance parameters after replacing the pretensioner). Clear the fault codes, perform the 'System Self-check' or 'Crash Test' function, and confirm the B1780 status changes to 'History Fault' or 'No Fault'. Finally, conduct a road test to verify.
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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.