AU
B1740-00

This DTC indicates that during the self-check, the SRS (Supplemental Restraint System) control module detects, through its internal diagnostic circuit, an open circuit in the left rear side airbag (left curtain airbag or seat side airbag) communication line, or the airbag module initialization resistance falls outside the normal range (typically 2 — Seal U

Safety System

This DTC indicates that during the self-check, the SRS (Supplemental Restraint System) control module detects, through its internal diagnostic circuit, an open circuit in the left rear side airbag (left curtain airbag or seat side airbag) communication line, or the airbag module initialization resistance falls outside the normal range (typically 2.0-3.0 ohms).

Consequently, the SRS module cannot confirm the physical presence or electrical connection integrity of the airbag, and the system registers the airbag as "not present".

In a collision, this airbag may fail to deploy, disabling side impact protection for the left rear passenger.

Additionally, the SRS system enters fail-safe mode, which may alter the deployment logic of the entire airbag system and illuminate the instrument cluster airbag fault warning lamp.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left rear side airbag wiring harness connector loose, disconnected, or making poor contact (common after seat adjustment, B-pillar trim panel removal/installation, or kicks from rear passengers)
  • 2Open circuit or abnormal resistance in the airbag module internal squib (internal airbag fault or aging)
  • 3Open circuit, short circuit due to abrasion, or short to ground in the wiring harness from the SRS module to the left rear airbag (repeated bending at the seat track or B-pillar sill breaks the copper wires).
  • 4SRS control module internal diagnostic circuit fault (outdated software version or damaged hardware sampling circuit)
  • 5Previous side impact, water wading, or vehicle submersion causing corrosion or water ingress at the airbag connector, or damage to the wiring harness insulation.
What To Do
  • 1
    Use the BYD VDS or a dedicated diagnostic tool to read the fault code. Confirm B1740-00 is a Current DTC, not a history DTC, and check the voltage and ambient temperature in the freeze frame data.
  • 2
    Disconnect the 12V battery negative terminal and wait at least 90 seconds to discharge the residual charge in the SRS capacitor to ensure safety and prevent accidental airbag deployment.
  • 3
    Locate the left rear side airbag (on Qin series models, usually inside the left B-pillar trim panel or on the side of the left rear seat). Verify the dedicated yellow connector is fully locked. Inspect the terminals for oxidation, backed-out pins, or deformation.
  • 4
    Use a multimeter to measure the airbag wiring harness continuity: the circuit resistance between the SRS module connector and the airbag connector must be less than 1 ohm, the insulation resistance to ground must be greater than 1M ohm, and the short-to-power check must read 0V.
  • 5
    Measure the airbag module resistance (via the wiring harness or direct connection). The standard value is 2.0±0.3 ohms. High resistance indicates an open circuit; low resistance indicates a short circuit. If the resistance is abnormal, replace the airbag assembly.
  • 6
    If the wiring harness has an open or short circuit, repair and rewrap the harness. If the connector is damaged, replace the dedicated yellow airbag connector and ensure the locking tab is secure.
  • 7
    Reconnect all connectors and connect the negative battery terminal. Use the diagnostic tool to clear the fault code and perform an SRS system self-test. Verify the fault code does not return and the warning light turns off.
  • 8
    Verify airbag system function (use the diagnostic tool to read the live data stream and confirm the left rear side airbag status displays 'Normal' instead of 'Not Present').
Real-World Cases
BYD DTC AI Analysis

Seat adjustment dislodged the airbag connector

✓
A 2017 Qin EV300 had the airbag warning light on steady. Read fault code B1740-00. Inspection found that frequent forward and backward adjustment of the left rear seat by passengers had loosened the side airbag harness connector under the seat. Reconnected the connector and secured the harness clip, then cleared the code. The fault code did not return.
BYD DTC AI Analysis

B-pillar wiring harness wear caused an open circuit.

✓
2018 BYD Qin EV450 had DTC B1740-00. Removed the left rear B-pillar trim panel and found the curtain airbag wiring harness insulation had worn through at the junction between the B-pillar and the body sheet metal. Prolonged vibration had damaged the insulation, and some copper wires were broken, causing an intermittent open circuit. Repaired the harness, added an anti-chafing sleeve, and resolved the fault.
BYD DTC AI Analysis

Corroded airbag connector on water-damaged vehicle

✓
A 2017 Qin 100 drove through water and stored DTC B1740-00. Inspection found mud and water residue inside the left rear side airbag connector (yellow plug); green corrosion on the terminals caused high contact resistance (measured 8.5 ohms). After cleaning the terminals and applying electronic protectant, resistance returned to normal, resolving the fault.
BYD DTC AI Analysis

Internal igniter fault in airbag module

✓
2017 BYD Qin 80 repeatedly set B1740-00. Harness continuity checked normal; connectors OK. Direct resistance measurement at the left rear side airbag module: infinite (open circuit). Determined internal airbag igniter circuit open. Replaced left rear side airbag assembly. System self-test passed.
BYD DTC AI Analysis

SRS module coding error after accident repair

✓
After accident repairs, a Qin EV300 stored DTC B1740-00. A check found the repair shop had replaced the SRS control module but coded it incorrectly. This base model lacks rear side airbags, yet the module had high-spec coding. Recoding and reconfiguring the SRS module cleared the fault code.
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.