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 8

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 Atto 8 indicates a high-severity SRS fault: a short to ground in the right middle-row seat belt pretensioner circuit. This can disable related airbag and pretensioner functions and keep the airbag warning light on. Common causes include damaged under-seat wiring 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 from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Under-seat wiring harness wear: Frequent fore-aft movement of the right middle-row seat (especially sliding-rail types) chafes the pretensioner harness insulation against the seat frame or guide rail edge. The exposed wire contacts metal body parts, creating a short to ground.
  • 2Connector water ingress and corrosion: Vehicle wading or interior cleaning allows liquid to enter 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: The pretensioner igniter inside the seat belt retractor develops internal coil insulation failure due to manufacturing defects, aging, or moisture ingress, causing a short to the housing (ground).
  • 4Improper accident repair: After a collision, the pretensioner deployed but the wiring harness was not replaced, or bolts/clips crushed the harness insulation due to improper securing during repair.
  • 5SRS ECU false detection (less common): 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 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 (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 sheath 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 between each terminal and body ground (normal value: infinite/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. Closely inspect the wiring harness within the seat's fore-and-aft travel range. Peel back 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 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 the pretensioner separately.
  • 7
    System reset: Restore all connections and turn on the power. Use the diagnostic tool to clear the fault code. Perform 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 resistance value of this circuit 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 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.