AU
B1740

DTC B1740 indicates the Airbag Control Unit (ACU) detects an open circuit in the Left Rear Side Airbag during the self-check, or the system configuration marks the airbag module as 'not present' — Seal 6 EV

Safety System

DTC B1740 indicates the Airbag Control Unit (ACU) detects an open circuit in the Left Rear Side Airbag during the self-check, or the system configuration marks the airbag module as 'not present'.

Hardware causes typically include an open circuit between the ACU and the left rear side airbag (resistance exceeds the threshold, typically >6Ω) or an internal open circuit within the airbag module itself.

Software configuration issues occur when the vehicle configuration code (VCU configuration) mismatches the actual hardware.

Examples include configuring a low-spec vehicle with high-spec parameters or installing a seat assembly without a side airbag.

This fault prevents the side airbag from deploying during a collision, severely compromising side-impact protection.

The SRS system also illuminates the instrument cluster airbag warning lamp and may disable the entire airbag system to enter safety mode.

The B1740 fault code on the Seal 6 EV indicates a medium-severity problem with the left rear side airbag circuit or configuration. The Airbag Control Unit may detect an open circuit, often caused by a loose under-seat airbag connector, poor pin contact, or a faulty side airbag module. This can stop the airbag from deploying. 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 — Seal 6 EV
  • 1Loose, disconnected, or poor contact at the left rear seat side airbag wiring harness connector: Frequent fore-and-aft seat adjustment or folding can loosen the yellow airbag plug under the seat, or pin oxidation can cause high resistance.
  • 2Airbag module fault: Left rear side airbag internal igniter open circuit. Typical causes include airbag aging, moisture ingress, or failure to replace a previously deployed airbag.
  • 3Physical damage to the wiring harness: Seat frame crushing, rodent bites, or seat modifications damaged the airbag wiring harness inside the seat, causing an open circuit.
  • 4Vehicle configuration error: Failure to reconfigure SRS system parameters using a diagnostic tool after replacing the seat assembly with one without a side airbag (e.g., lower-spec seat), or incorrect ACU coding.
  • 5Airbag Control Unit (ACU) fault: An ACU internal monitoring circuit fault falsely reports the left rear side airbag status. Although rare, inspect the ACU.
What To Do
  • 1
    Safety Check and Preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds for the SRS capacitor to discharge to prevent accidental airbag deployment. Remove the left rear seat assembly to access the airbag assembly.
  • 2
    Visual inspection and connection confirmation: Verify the yellow airbag connector under the seat (usually marked 'SRS' or 'AIRBAG') is fully locked. Inspect the plug for signs of water ingress, corrosion, or backed-out pins. Disconnect and reconnect the plug; listen for a 'click' to confirm the lock engages.
  • 3
    Diagnostic tool data stream analysis: Connect the VDS or a dedicated diagnostic tool, read the SRS system data stream, and check the 'left rear side airbag resistance value'. The normal range is typically 2.0-3.5Ω. If the tool displays '>10Ω' or 'Open', this confirms an open circuit.
  • 4
    Circuit continuity test: Use a multimeter to measure harness continuity between the airbag connector and the ACU (pin-to-pin resistance <1Ω), and measure insulation to ground (>1MΩ). Inspect harness wear points at the seat hinge.
  • 5
    Airbag module independent test: Disconnect the airbag connector and connect a dedicated airbag simulator (2.7Ω resistor) in its place. If the fault code changes to "resistance too low" or disappears, the airbag module is faulty. Replace the left rear seat side airbag assembly.
  • 6
    Configuration verification and calibration: If the hardware is normal, enter the SRS system 'Coding/Configuration' function. Check the vehicle configuration table (view 'Seat Airbag Configuration' in VDS) and verify it matches the actual vehicle. If the configuration is incorrect, rewrite the correct configuration code.
  • 7
    System reset and verification: Clear the fault code, reconnect the battery, turn the ignition switch to the ON position, and verify the instrument cluster airbag warning light turns off. Perform three ignition cycle self-checks and confirm B1740 does not return. Finally, perform a simulated crash test (use the diagnostic tool to trigger the sensor test; do not perform an actual impact) to verify normal system communication.
Real-World Cases
BYD DTC AI Analysis

Case: Seat adjustment causing connector to come loose

✓
A 2020 BYD Song MAX with 30,000 km had the airbag warning light suddenly come on. The scan showed DTC B1740. The owner reported the fault appeared after folding the rear seats to load large items. The technician removed the left rear seat and found the yellow 2-pin airbag connector underneath not fully latched; its latch had broken, causing poor contact. Replaced the connector and recrimped the terminals. Fault resolved. Analysis: frequent seat angle adjustment caused the connector to loosen under stress.
BYD DTC AI Analysis

Aftermarket seat replacement causes configuration error.

✓
After replacing the left rear seat assembly with an aftermarket unit (without side airbag), a 2019 BYD Yuan EV illuminated the airbag warning light and logged DTC B1740. Using a VDS diagnostic tool to access the SRS system revealed the 'Left rear side airbag present' option was set to 'Present', which did not match the actual hardware. After changing this setting to 'Not present' via the configuration function (or fitting an OEM seat with the airbag) and clearing the fault code, the system returned to normal. Note: Some BYD models require reconfiguring airbag parameters using a diagnostic tool after hardware changes.
BYD DTC AI Analysis

Wiring harness wear causing open circuit case

✓
A 2021 BYD Tang intermittently lit the airbag warning light after driving on rough roads. The scan tool showed B1740 as a stored historical fault. Removing the left rear seat backrest revealed the side airbag harness insulation had chafed through at the seat frame hinge. Several copper strands were partially fractured, causing an intermittent open circuit. The harness was repaired by soldering the connections and insulating with heat-shrink tubing. Corrugated tubing was added at the worn area for protection, and the harness was rerouted and secured to prevent contact with the metal frame. The fault was completely fixed.
BYD DTC AI Analysis

Airbag Module Internal Open Circuit Case

✓
A 2019 BYD Qin petrol version developed DTC B1740 following accident repairs (left rear door collision). Inspection revealed no external damage and the wiring harness had normal continuity. Using an airbag simulator in place of the original airbag changed the fault code characteristics, confirming the left rear seat side airbag internal igniter had an open circuit from impact damage. Replaced the left rear seat side airbag assembly (requires seat trim removal and anti-static precautions). Secured the new airbag module to the specified torque (typically 9–11 Nm). Fault resolved.
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.