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 — Seal 6 EV

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.

The B1782 fault code on the Seal 6 EV indicates a high-severity short-to-ground fault in the right middle-row seat belt pretensioner circuit. This can disable related SRS protection and keep the airbag warning light on, meaning the pretensioner may not work in a crash. Common causes include under-seat harness damage from seat movement or water ingress/corrosion in the yellow SRS connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 4 recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Under-seat harness wear: Frequent fore-and-aft movement of the right middle-row seat (especially sliding-rail seats) causes the seat frame or guide rail edge to wear through the pretensioner 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 seeps into the yellow SRS connector under the middle-row seat (usually located at the base of the B-pillar or seat crossmember), causing a short circuit between terminals or a short to ground.
  • 3Pretensioner internal fault: Manufacturing defects, aging, or moisture ingress cause internal coil insulation failure in the seat belt retractor pretensioner igniter, resulting in a short to the housing (ground).
  • 4Improper accident repair: Pretensioner deployed after a collision but wiring harness not replaced, or improper harness securing during repair caused bolts/clips to crush the insulation.
  • 5SRS ECU false reporting (uncommon): A fault in the control unit internal sampling circuit causes a false short circuit detection. Rule out wiring and component faults first.
What To Do
  • 1
    Safety preparation: Switch the vehicle to 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). Check for accompanying fault codes (such as B1781).
  • 3
    Visual inspection: Check the right second-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 fixing 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 value: infinite/OL; short circuit: < 1 Ω).
  • 5
    Wiring harness inspection: If the pretensioner unit resistance is normal, measure the harness side. Continuity to ground at one terminal indicates a damaged circuit shorted to ground. Inspect the wiring harness within the seat's fore-and-aft movement range. Open the corrugated conduit and check for exposed copper strands 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 20mm 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. Perform the 'SRS system self-check' or 'crash sensor calibration' procedure. Verify B1782 does not return and the instrument cluster airbag warning light turns off. Read the data stream to confirm the circuit resistance value has returned 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 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.