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 U

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 U indicates a high-severity SRS fault: a short to ground in the right middle-row seat belt pretensioner circuit. The airbag warning light may stay on, and the pretensioner or related restraints may not work in a crash. Common causes include under-seat harness damage from seat movement or water/corrosion in the yellow SRS connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Under-seat harness wear: Frequent fore-and-aft movement of the right middle-row seat (especially seats with sliding rails) causes the seat frame or guide rail edge to chafe through the pretensioner harness insulation, allowing it to contact metal body components and create a short to ground.
  • 2Connector water ingress and corrosion: Liquid enters the yellow SRS connector under the middle-row seat (usually located at the base of the B-pillar or on the seat crossmember) during water wading or interior cleaning, 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, creating a short to the housing (ground).
  • 4Improper accident repair: After a vehicle collision, the pretensioner deployed but the wiring harness was not replaced, or bolts or clips crushed the harness insulation due to improper securing during repair.
  • 5SRS ECU false detection (less common): An internal sampling circuit fault in the control unit causes a false short circuit detection. Rule out wiring and component faults first.
What To Do
  • 1
    Safety preparation: Set 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), and 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: 2.0-3.0Ω). Then measure the resistance from each terminal to body ground (normal: infinity/OL; short circuit: < 1Ω).
  • 5
    Wiring harness inspection: If the pretensioner body resistance is normal, measure the harness side. Continuity to ground on one terminal indicates a damaged wire shorted to ground. Carefully inspect the wiring harness within the seat's forward and rearward 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 at least a 20mm clearance 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 the pretensioner separately.
  • 7
    System reset: Restore all connections, switch on the power, and use the diagnostic tool to clear the fault code. Execute the 'SRS system self-check' or 'crash sensor calibration' procedure. Confirm B1782 does not reappear 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 Seal U Fault Codes
B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.