AU
B1731

DTC B1731 indicates the Supplemental Restraint System (SRS) control unit detects the igniter circuit resistance for the left second-row side airbag module (typically located inside the left B-pillar trim panel or on the side of the left rear seat) falls below the normal threshold (BYD models typically specify 1 — Seal U

Safety System

DTC B1731 indicates the Supplemental Restraint System (SRS) control unit detects the igniter circuit resistance for the left second-row side airbag module (typically located inside the left B-pillar trim panel or on the side of the left rear seat) falls below the normal threshold (BYD models typically specify 1.5-2.5Ω; refer to the workshop manual for exact specifications).

Low resistance indicates an abnormal low-resistance path in the circuit.

Potential causes include an internal short circuit in the igniter, a wiring harness short to ground, a short between connector terminals, or a faulty internal sampling circuit in the SRS ECU.

This fault forces the SRS into fail-safe mode.

During a side impact, the airbag may fail to deploy, or in extreme cases, trigger inadvertently.

The instrument panel airbag warning light remains illuminated, indicating limited occupant protection system functionality.

The B1731 fault code on the Seal U indicates the SRS control unit has detected low resistance in the left second-row side airbag igniter circuit. Severity is medium because the airbag system may not protect correctly and the warning light will stay on. Common causes include a shorted airbag igniter or damaged wiring insulation. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left middle row side airbag module internal igniter short circuit (component aging or impact damage)
  • 2Damaged wiring harness insulation causing a short to ground or a short between positive and negative wires (commonly resulting from friction during movement at the seat adjustment mechanism or B-pillar hinge).
  • 3Water ingress, corrosion, or terminal deformation in the airbag connector causing abnormal continuity between terminals (common after vehicle wading or due to poor sealing).
  • 4Frequent fore-and-aft seat adjustment or removal and installation pinches or chafes the wiring harness, exposing the copper wire and causing a short circuit.
  • 5Internal sampling resistor or A/D conversion circuit fault in the SRS control unit (less common; typically occurs with multiple simultaneous airbag fault codes)
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read all fault codes and freeze frame data. Confirm B1731 is a current fault, not a history fault. Record the environmental conditions when the fault occurred.
  • 2
    Perform the airbag system safe power-down procedure: turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds (to fully discharge the SRS capacitor). Before disconnecting the airbag module connector, short the wiring harness terminals on the SRS ECU side to prevent accidental deployment.
  • 3
    Locate the left middle-row side airbag module (depending on model year, this is inside the left B-pillar trim panel or on the side of the left rear seat). Carefully remove the trim panel and inspect the wiring harness for signs of abrasion, crushing, or water ingress.
  • 4
    Disconnect the airbag module connector. Use a dedicated low-current ohmmeter (or a digital multimeter on the low-resistance setting) to measure the resistance between the airbag module terminals. Normal resistance is 1.5-2.5 Ω. A reading below 1.0 Ω indicates an internal module short circuit.
  • 5
    Measure the wiring harness side connector: measure the resistance to ground for each of the two wires (should be greater than 1MΩ) and the resistance between the wires (should be greater than 1MΩ or open circuit). A low resistance value indicates a short circuit in the wiring harness. Inspect along the wiring route, focusing on wear-prone areas such as the seat rails, B-pillar trim clips, and under the carpet.
  • 6
    Check the connector terminals for backed-out pins, corrosion, verdigris, or foreign matter. If necessary, clean with electrical contact cleaner and re-secure the terminals.
  • 7
    If the wiring harness is damaged, repair it with heat-shrink tubing or replace the wiring harness assembly. If the airbag module resistance is abnormal, replace it with an OEM airbag module (Note: The airbag module is a safety component; replace it with a part having the same part number).
  • 8
    After completing the repair, reconnect all connectors (ensure a locking click), reconnect the battery, turn the ignition switch to ON, clear the fault code using VDS, and perform the SRS system self-check cycle.
  • 9
    Perform a road test to verify the airbag warning light turns off after the self-test, DTC B1731 does not return, and related functions operate normally.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM seat adjustment caused wiring harness wear and short circuit

✓
The instrument cluster occasionally illuminated the airbag warning light. VDS read DTC B1731 (left second row side airbag resistance low). Removing the left second row seat revealed that the side airbag wiring harness had chafed against the seat sliding rail, where long-term friction damaged the insulation, exposing copper wire that contacted the seat frame and created a short to ground. Repair: Cut out the damaged section, rewrapped with waterproof heat shrink tubing, relocated the harness fixing points away from moving parts, and fitted abrasion-resistant sleeves. Cleared the DTC and road-tested for one week with no recurrence.
BYD DTC AI Analysis

BYD Song MAX B-pillar water ingress caused connector corrosion

✓
The customer reported the airbag warning light remained constantly on when starting the vehicle after rain. Diagnosis revealed active DTC B1731. Inspection of the airbag connector inside the left B-pillar trim found the seal had deteriorated, allowing rainwater ingress. White oxide on the terminal surfaces caused a micro-short circuit, reducing resistance to 0.8Ω. Repair: Thoroughly cleaned the terminals with precision electrical cleaner and non-woven cloth, applied special conductive protective grease, replaced the waterproof seal, and installed a dust filter mesh at the B-pillar base drain hole to prevent further water ingress.
BYD DTC AI Analysis

Internal short circuit in BYD Yuan EV airbag module

✓
Vehicle had no collision history, but the dashboard kept displaying an airbag fault. Measured the left second-row side airbag module resistance at 0.6Ω, far below the standard value. Confirmed an internal igniter short circuit inside the module. The car had previously undergone interior deep cleaning at an external detailing shop; cleaning agent likely seeped into the airbag module. Replaced the module with a genuine part. The new module resistance measured 2.1Ω (normal). After installation and coding, the fault cleared.
BYD DTC AI Analysis

BYD Qin petrol version SRS ECU software false positive

✓
Vehicle logged multiple contradictory DTCs including B1731 and B1732 (high resistance in same airbag circuit) with intermittent symptoms. Checked wiring harness and airbag module – both normal. Suspected drift in SRS control unit sampling circuit. Checked technical bulletin: this model year has an ECU software defect that causes false resistance errors at certain temperatures. Fix: Updated SRS ECU software to latest version (check TIS for version number). After update, DTCs cleared and haven't returned.
BYD DTC AI Analysis

BYD Tang aftermarket seat covers installed incorrectly

✓
Customer reported DTC B1731 after installing aftermarket seat covers. Inspection found that when securing the seat cover fasteners, the installer drove a screw through the side airbag harness sheath, shorting two signal wires together. Repair: Removed the improperly installed fasteners, replaced the damaged harness section (full run from main harness to airbag module), rerouted the wiring to specification and secured it with genuine harness clips. Educated the customer to avoid installing rigid decorative items in airbag deployment zones.
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.