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 — Qin Plus

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.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Internal igniter short circuit in left middle row side airbag module (component aging or impact damage)
  • 2Damaged wiring harness insulation causing a short to ground or a short between positive and negative wires (commonly due to friction from movement at the seat adjustment mechanism or B-pillar hinge).
  • 3Water ingress, corrosion, or deformed terminals at the airbag connector causing abnormal continuity between terminals (common after vehicle wading or seal failure).
  • 4Frequent fore-and-aft seat adjustment or seat removal and installation pinches or chafes the wiring harness, exposing copper wire and causing a short circuit.
  • 5SRS control unit internal sampling resistor or A/D conversion circuit fault (less common; usually 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. Verify B1731 is a current fault, not a history fault, and 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 the 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 wear, pinching, or water ingress.
  • 4
    Disconnect the airbag module connector. Measure the resistance between the airbag module terminals using a dedicated low-current ohmmeter (or a digital multimeter set to the low-resistance range). 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 of each wire to ground (should be greater than 1 MΩ) and the resistance between the two wires (should be greater than 1 MΩ 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 a genuine airbag module (Note: The airbag module is a safety-critical part; install a replacement with the same part number).
  • 8
    After completing the repair, reconnect all connectors (listen for the locking click), reconnect the battery, turn the ignition switch to the ON position, 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 self-check, DTC B1731 does not recur, 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 Qin Plus 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.