AU
B1782

DTC B1782 indicates the SRS (Supplemental Restraint System) control unit detects a short-to-ground fault in the right middle-row seat belt pretensioner circuit — Atto 3

Safety System

DTC B1782 indicates the SRS (Supplemental Restraint System) control unit detects a short-to-ground fault in the right middle-row seat belt pretensioner circuit.

Specifically, the resistance between the pretensioner squib positive or negative circuit and body ground falls below the system threshold (typically < 1Ω), causing the ECU to flag a circuit fault.

This fault forces the SRS into a degraded protection mode, disables the right middle-row and associated airbag and pretensioner functions, and continuously illuminates the airbag warning light on the instrument cluster.

During a collision, the pretensioner may fail to deploy and tighten the seat belt.

This significantly reduces occupant protection and constitutes a severe driving safety fault.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Wiring harness wear under the seat: Frequent forward and backward movement of the right middle-row seat (especially sliding-rail seats) causes the seat frame or guide rail edge to wear through the pretensioner wiring harness insulation. The harness contacts metal body parts, creating a short to ground.
  • 2Connector water ingress and corrosion: During vehicle wading or interior cleaning, liquid enters the yellow SRS connector under the middle-row seat (usually at the base of the B-pillar or seat crossmember), causing a short circuit between terminals or from a terminal to ground.
  • 3Pretensioner assembly internal fault: Manufacturing defects, aging, or moisture ingress cause internal coil insulation failure in the seat belt retractor pretensioner igniter, resulting in a short circuit to the housing (ground).
  • 4Improper accident repair: After a collision, the pretensioner deployed but the wiring harness was not replaced, or improper securing during repair caused bolts/clips to crush the insulation.
  • 5SRS ECU false detection (less common): An internal fault in the control unit sampling circuit causes a false short circuit detection. Rule out wiring and component faults first.
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use BYD VDS or Launch X-431 to read fault codes, confirm B1782 is a current fault (Active), record freeze frame data (ambient temperature and voltage), and check for associated fault codes (e.g., B1781).
  • 3
    Visual inspection: Check the right middle-row seat belt pretensioner connector (yellow plug, usually located under the seat or inside the B-pillar trim) for signs of water ingress, corrosion, or deformed pins; check the wiring harness sleeve at the seat slide rail mounting point for damage.
  • 4
    Resistance measurement: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the two terminals on the pretensioner side (normal value: 2.0-3.0 Ω). Then measure the resistance from each terminal to body ground (normal: infinite/OL; short circuit: < 1 Ω).
  • 5
    Wiring harness inspection: If the pretensioner unit resistance is normal, measure the harness side. Continuity to ground on one terminal indicates wire damage and a short to ground. Focus the inspection on the wiring harness within the seat's fore-and-aft travel range. Peel back the corrugated conduit and check for exposed copper wire contacting the seat frame.
  • 6
    Repair verification: If the wiring harness is damaged, repair it with heat-shrink tubing or waterproof tape and re-secure it. Maintain a clearance of more than 20 mm from metal components. If the pretensioner has an internal short circuit, replace the seat belt retractor assembly (including the pretensioner). Do not disassemble or repair it separately.
  • 7
    System reset: Restore all connections and turn on the power. Clear the fault code using the diagnostic tool. Execute the 'SRS system self-check' or 'crash sensor calibration' procedure. Confirm DTC B1782 does not return and the instrument cluster airbag warning light turns off. Read the data stream to confirm the circuit resistance value returns to the normal range.
Real-World Cases
BYD DTC AI Analysis

Song MAX second-row seat rails chafed through wiring harness, causing intermittent short circuit

✓
A 2019 Song MAX stored DTC B1782 intermittently. Inspection found the right middle-row seat uses an independent sliding design; the sharp rear edge of the seat runner wore through the pretensioner wiring harness sheath, causing the copper wires to occasionally contact the seat frame. Repaired the harness, rewrapped it with high-temperature resistant corrugated tubing, repositioned the clips to avoid runner interference, and eliminated the fault.
BYD DTC AI Analysis

Tang DM SRS connector corroded and shorted after wading

✓
2021 Tang DM showed an airbag warning on the instrument cluster after driving through floodwater. Scan tool read DTCs B1782 and B1781 (second row left). Disassembly revealed the carpet beneath the second row seats saturated, with green corrosion on the terminals inside two yellow SRS connectors causing a short to ground. Cleaned the connectors with electronic cleaner, blow-dried them, and applied conductive protectant. Replaced the carpet waterproof underlay and cleared the fault codes. System returned to normal.
BYD DTC AI Analysis

Yuan EV Seatbelt Pretensioner Internal Igniter Short Circuit Replacement Case

✓
A 2019 Yuan EV set DTC B1782 after accident repairs. Wiring harness checked normal. With the pretensioner connector disconnected, resistance between the pretensioner body terminals and casing measured 0.3Ω (should be infinite), confirming internal moisture had caused a short. Replaced the right middle row seat belt retractor assembly (P/N: 6A-8217060), cleared the code, and the SRS system passed self-test. After replacement, run 'configuration coding write' in the diagnostic tool to match the new component parameters.
BYD DTC AI Analysis

Improperly secured wiring harness after Qin Pro accident repair

✓
2020 BYD Qin petrol: After collision repair, the customer reported the airbag warning light on. Scan revealed DTC B1782. Reviewing the repair history showed the right rear seat pretensioner harness had been pinched by a seat mounting bolt during reinstallation, damaging the insulation and shorting to earth. Rerouted the harness, fitted a protective sleeve and replaced the damaged section. Fault resolved. After body repairs involving SRS components, verify harness routing against the factory wiring diagram.
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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.