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' — Atto 8

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.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 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 connector under the seat, or pin oxidation can cause high resistance.
  • 2Airbag module fault: Left rear side airbag internal igniter open circuit. Common causes include airbag aging, moisture ingress, or failure to replace a previously deployed airbag.
  • 3Physical damage to the wiring harness: Seat frame crushing, rodent chewing, or seat modification 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 side airbags (e.g., low-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 uncommon, 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 check: 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 recessed pins. Disconnect and reconnect the connector; listen for a 'click' to confirm locking.
  • 3
    Diagnostic tool data stream analysis: Connect the VDS or 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. A reading of ">10Ω" or "Open" confirms an open circuit.
  • 4
    Circuit continuity test: Use a multimeter to measure wiring harness continuity between the airbag connector and the ACU (pin-to-pin resistance must be <1Ω) and measure insulation to ground (must be >1MΩ). Focus inspection on wiring harness wear points at the seat hinge.
  • 5
    Airbag module standalone test: Disconnect the airbag connector and install a dedicated airbag simulator (2.7Ω resistor) in place of the airbag. 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, access the SRS system 'Coding/Configuration' function. Verify the vehicle configuration table (check the 'Seat Airbag Configuration' item in the VDS) 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 ON, and verify the instrument cluster airbag warning light turns off. Perform three ignition cycle self-checks to confirm DTC B1740 does not return. Finally, perform a simulated crash test (use the diagnostic tool to trigger the sensor test; do not physically impact the vehicle) 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 Atto 8 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.