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 U

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 U indicates a medium-severity fault with the left rear side airbag circuit, usually an open circuit or incorrect vehicle configuration showing the airbag as not present. Common causes include a loose or corroded under-seat airbag connector, damaged wiring, or a faulty side airbag module. Visit an authorised dealer for diagnosis, configuration checks, 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 U
  • 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: Open circuit in the left rear side airbag igniter. 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 chewing, 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 a unit without side airbags (e.g., lower-spec seat), or incorrect ACU coding.
  • 5Airbag Control Unit (ACU) fault: Internal ACU monitoring circuit fault falsely reports the left rear side airbag status. Rare, but requires troubleshooting.
What To Do
  • 1
    Safety Check and Preparation: Disconnect the 12V battery negative terminal. 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 plug, confirming a locking 'click'.
  • 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 should be <1Ω). Measure insulation to ground (should be >1MΩ). Inspect the wiring harness at the seat hinge for wear.
  • 5
    Airbag component standalone test: Disconnect the airbag connector and connect 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, enter the SRS system 'Coding/Configuration' function. Check the vehicle configuration table (view the 'Seat Airbag Configuration' item 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, and turn the ignition switch to the ON position. 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 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 U Fault Codes
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.