AU
B1765

DTC B1765 indicates the resistance in the right front side curtain airbag (RH Side Curtain Airbag) ignition circuit exceeds the normal threshold calibrated by the SRS ECU (typically 2 — Seal U

Safety System

DTC B1765 indicates the resistance in the right front side curtain airbag (RH Side Curtain Airbag) ignition circuit exceeds the normal threshold calibrated by the SRS ECU (typically 2.0-3.0Ω, with an upper limit of approximately 5-6Ω).

This constitutes an airbag system loop integrity fault, indicating a high-resistance condition (approaching an open circuit) in the circuit between the SRS control unit and the right front side curtain airbag inflator.

This fault causes the SRS ECU to determine the airbag cannot deploy normally, potentially failing to provide lateral head protection during a collision.

The system illuminates the airbag warning light and may disable the entire airbag system.

Although some OBD-II standards define B1765 as a seat circuit fault, the BYD SRS system (specifically in models like the Song MAX and Qin) defines this code as abnormal right curtain airbag resistance.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal open circuit or aging of the right front side curtain airbag igniter, causing internal resistance to exceed 6Ω.
  • 2Loose connection, oxidation, or poor contact at the airbag wiring harness connector in the A-pillar or roof side rail, causing contact resistance.
  • 3Broken (or partially broken) internal copper wire in the airbag wiring harness where it passes through the door hinge or body bend, causing increased resistance.
  • 4SRS ECU internal sampling circuit fault or abnormal software calibration causing a false high resistance reading.
  • 5Airbag wiring harness damaged or pinched during vehicle modifications (such as installing roof ambient lighting or removing/installing the A-pillar trim)
What To Do
  • 1
    Use BYD dedicated diagnostic tool VDS2000/VDS2100 to read the complete fault codes and freeze frame data. Check for related fault codes such as B1764 (resistance too low) or B1766 (not present).
  • 2
    Perform the safe power-down procedure: Turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds for the SRS capacitor to fully discharge.
  • 3
    Remove the right front A-pillar trim panel and the front roof trim panel. Visually inspect the right front side curtain airbag wiring harness connector (usually located above the A-pillar or at the front of the roof side rail) for looseness, water ingress, oxidation, or pin corrosion. If necessary, clean the connector with electrical contact cleaner and reconnect it securely.
  • 4
    Use the SRS system tester to measure the continuity and resistance of the wiring harness between the SRS ECU and the airbag (do not measure the airbag directly with a multimeter to prevent accidental deployment). Verify the harness resistance is less than 1 Ω.
  • 5
    If the wiring harness tests normal, connect an airbag simulator (2Ω substitute resistor) to the circuit. Clear the fault code, power on again, and perform a self-check. If the fault code disappears, the airbag module is faulty. Replace the right front side curtain airbag module.
  • 6
    After replacement, reconnect all connectors and restore power. Clear the fault code using the diagnostic tool and perform an SRS system self-check (DTC Clear & System Check). Verify the fault code does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Oxidation on the Song MAX right front side curtain airbag connector caused high resistance.

✓
A 2019 BYD Song MAX with 30,000 km displayed a constant airbag warning light. Scanning revealed DTC B1765. Inspection found the vehicle had previously undergone front windshield replacement. During A-pillar trim removal and refitting, the right front side curtain airbag connector was not fully seated and the contacts had oxidized. Cleaning the terminals, applying conductive grease, and reconnecting securely restored resistance to 2.3 ohms and resolved the fault.
BYD DTC AI Analysis

Qin Pro: Wiring harness damaged after accident repair, causing B1765

✓
After a right-side scrape accident, the dealership replaced the right front door and A-pillar trim on a 2020 BYD Qin petrol. One week after delivery, the airbag warning light came on. Diagnosis revealed DTC B1765. Further inspection found a trim clip had pinched the airbag wiring harness during the repair, partially fracturing the internal copper wires without completely severing them. This resulted in high resistance (measured at 8.5Ω). Repaired the harness and rerouted the wiring to resolve the fault.
BYD DTC AI Analysis

Right front airbag connector corroded after water ingress

✓
Song MAX airbag warning light illuminated after driving through water in heavy rain. VDS showed DTC B1765. Removed the right front A-pillar trim and found water in the airbag harness connector; green corrosion on the copper pins increased contact resistance to 12Ω. Cleaned the contacts with precision electronic cleaner, dried them with compressed air, applied insulating silicone grease, and replaced the waterproof seal ring. Cleared the fault code and the system returned to normal.
BYD DTC AI Analysis

SRS ECU software error caused false high-resistance fault

✓
A 2020 Qin logged an intermittent B1765 DTC during cold starts; the code cleared after driving. Airbag resistance measured 2.1Ω (normal) and the wiring harness showed no faults. A technical service bulletin revealed this production batch had SRS ECU software with a sampling error that could falsely report high resistance in low temperatures. The dealership upgraded the SRS control unit software to the latest version, eliminating the fault.
Other Seal U 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.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.
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.