AU
B1742

DTC B1742 indicates an abnormal short circuit between the left rear side airbag ignition loop (typically installed in the left rear seat backrest or C-pillar) and the vehicle power supply positive (B+) — Seal U

Safety System

DTC B1742 indicates an abnormal short circuit between the left rear side airbag ignition loop (typically installed in the left rear seat backrest or C-pillar) and the vehicle power supply positive (B+).

In the Supplemental Restraint System (SRS), the airbag module connects to the Airbag Control Unit (ACU) via two wires.

Normal wiring harness resistance measures approximately 2-3 ohms.

The diagnostic system triggers this fault code upon detecting a short to power in this circuit (voltage approaching 12V battery voltage instead of the normal low-voltage signal).

This fault is extremely dangerous.

The short circuit can cause unexpected airbag deployment while driving, severely injuring occupants.

Furthermore, the system enters protection mode and disables the airbag, preventing inflation during a collision and eliminating side-impact protection.

Additionally, the SRS illuminates the instrument cluster airbag warning light and may lock the entire airbag system, disabling all airbags.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness insulation wear under the seat or inside the B-pillar/C-pillar: Frequent seat fore-and-aft adjustment or friction during passenger ingress/egress damages the airbag wiring harness insulation, causing the wire core to directly contact the metal vehicle frame or power supply wiring.
  • 2Water ingress or corrosion at the under-seat connector: Spilled drinks, water seepage during car washing, or vehicle wading creates a conductive path or electrolytic corrosion between the airbag connector terminals, causing a short circuit between the pins.
  • 3Airbag module internal fault: Airbag inflator igniter (squib) insulation failure causing a short circuit between the bridgewire and housing, or internal circuit board fault.
  • 4SRS control unit (ACU) internal drive circuit damaged: The airbag drive transistor or related circuit inside the control unit shorted, causing the output terminal to continuously output a high level.
  • 5Harness damage from aftermarket modifications: Fixing screws pierce the harness or metal edges pinch the harness when installing seat covers, seat heating pads, dash cam wiring, or audio upgrades.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (some models require 3 minutes) to fully discharge the SRS backup power supply and prevent accidental airbag deployment during repair.
  • 2
    Fault confirmation and freeze frame retrieval: Use a dedicated diagnostic tool (such as BYD VDS2000/3000) to read the complete fault codes and freeze frame data. Record the vehicle status at the time of the fault (vehicle speed, temperature, etc.) to confirm if the fault is intermittent.
  • 3
    Visual and wiring harness inspection: Inspect the wiring harness in the left rear seat side airbag area (usually on the left side of the seat backrest) for obvious damage, crushing, or burn marks; inspect the yellow SRS connector under the seat for looseness, water ingress, or foreign objects.
  • 4
    Electrical measurement and isolation diagnosis: Disconnect the airbag module connector. Use a multimeter to measure the resistance/voltage from both terminals on the harness-side connector to body ground and to the 12V power supply to determine if the short circuit is on the harness side or the module side. Measure the resistance between the two airbag module terminals, and between the terminals and the housing (Normal values: >1 MΩ to power/ground, 2-3 Ω between terminals).
  • 5
    Section-by-section troubleshooting: If the wiring harness has a short to power, sequentially disconnect the intermediate connectors (usually located under the B-pillar or under the seat) from the ACU to the airbag module. Measure each section to pinpoint the short circuit.
  • 6
    Component replacement and repair: Based on diagnostic results, replace the damaged airbag module, repair the damaged wiring harness (use high-temperature wire of the same specification and apply double insulation), or replace the SRS control unit. Never wrap the SRS wiring harness with standard electrical tape.
  • 7
    System verification: Reconnect all connectors, connect the battery, use the diagnostic tool to clear the fault code, and perform the SRS system self-check. Perform a dynamic test (simulate the full seat adjustment range) to confirm the fault does not recur. Verify the instrument panel airbag warning lamp turns off after 6 seconds.
Real-World Cases
BYD DTC AI Analysis

Worn left rear seat wiring harness caused intermittent B1742 fault in Song MAX

✓
A 2019 Song MAX with 32,000 km showed an intermittent airbag warning light on the instrument panel. The scan tool retrieved DTC B1742 as an intermittent history code. The technician found the wiring harness retaining clip under the left rear seat rail had detached. The harness had chafed against the seat metal bracket, damaging the insulation and exposing the copper core. The exposed conductor intermittently touched the bracket; measurements showed low impedance between the bracket and battery positive, indicating an abnormal contact between the body harness and a power line elsewhere. Replaced the complete SRS harness assembly from the B-pillar to the seat (BYD part number: KBC-5823947). Rerouted the wiring and secured it using dedicated harness clips to prevent interference with seat moving parts. No recurrence after one month of follow-up.
BYD DTC AI Analysis

Tang DM seat modification caused airbag harness short to power

✓
A 2021 Tang DM owner reported the airbag warning light staying on with active fault code B1742. Aftermarket ventilated seats and leather seat covers had been fitted. The technician found the installer used excessively long self-tapping screws to secure the rear seat back cover panel, one of which pierced the left rear side airbag wiring harness. The screw contacted battery positive through the metal frame because the insulation on the aftermarket relay wiring was damaged. This shorted the airbag igniter circuit to positive via the screw. Repairs: Removed the offending screws. Replaced the pierced SRS harness section with BYD-certified high-temperature flame-retardant wire. Removed the aftermarket relay wiring and restored the original vehicle circuit. Replaced the left rear side airbag module, as the short may have damaged the internal igniter.
BYD DTC AI Analysis

SRS connector shorted from corrosion after Yuan EV wading

✓
A 2019 Yuan EV presented with the airbag warning light continuously illuminated after wading through deep floodwater. The diagnostic scan retrieved DTCs B1742 and B1740 (left front side airbag) along with multiple short-circuit fault codes. Inspection revealed the vehicle had driven through water deeper than the door sills, allowing water to penetrate the door seals and accumulate beneath the seats. The yellow 2-pin SRS connector located under the left rear seat showed obvious water staining and verdigris corrosion inside, causing short circuits between the terminals and between the terminals and the connector housing (the housing had established an abnormal connection to the power supply through the vehicle body). Repair procedure: Thoroughly dried the area beneath the seats, cleaned the connector using electronic cleaner, and replaced the corroded terminals (Part number: BYD-SRS-CONN-02). Applied protective wax inside the connector. Since the short circuit was brief, the airbag module tested undamaged. Retained the original module. Advised the owner to inspect the door drain holes for blockages.
BYD DTC AI Analysis

Qin Pro SRS control unit falsely reporting internal fault B1742

✓
A 2020 Qin Pro logged DTC B1742. Inspection found the left rear side airbag harness and connectors completely normal, with resistance to power exceeding 10 MΩ and airbag module resistance at 2.1 Ω (within specification). The fault code consistently returned after approximately 50 km of driving following each clear, with freeze frame data indicating the fault occurred while the vehicle was stationary. Further checks revealed the SRS control unit (ACU, located beneath the centre console) outputting abnormal voltage at the corresponding pin (continuous 12 V instead of the normal low-level scan signal). Diagnosed internal driver circuit breakdown within the ACU. Replaced the airbag control unit (part number: SC-3992847-B1), performed ACU coding and configuration using a diagnostic tool (entering the vehicle VIN and airbag configuration code), and carried out system calibration. This completely resolved the fault. This is a known quality issue affecting this batch of ACUs; check for any extended warranty coverage.
BYD DTC AI Analysis

Yuan Plus left rear side airbag module internal short circuit

✓
A 2022 Yuan Plus (DTC B1742 also applies to this platform) developed a constantly illuminated airbag warning light during normal use. Diagnosis confirmed B1742 as an active hard fault. After disconnecting the connector beneath the seat, the harness side measured no short to power. However, resistance between the two terminals of the airbag module (mounted inside the seat back) was 0.5 Ω (too low), and resistance to the module metal housing was 0 Ω (full continuity). Disassembly revealed the internal igniter bridge wire insulation had melted under high temperatures due to a manufacturing defect, causing a short to the housing. Repair: replace the left rear side airbag module assembly (part number YQ-5823947). Disconnect the battery and follow anti-static procedures during replacement. This case points to a supplier batch quality issue; check for any recalls or Technical Service Bulletins (TSBs).
Other Seal U 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.