AU
B1742-00

DTC B1742-00 indicates the SRS (airbag) control module detects an abnormally low-resistance short circuit between the Left Rear Side Airbag squib circuit and the vehicle positive power supply (+B, typically 12V battery voltage) — Seal U

Safety System

DTC B1742-00 indicates the SRS (airbag) control module detects an abnormally low-resistance short circuit between the Left Rear Side Airbag squib circuit and the vehicle positive power supply (+B, typically 12V battery voltage).

Under normal conditions, high resistance isolates the airbag squib circuit from both power and ground.

The SRS module internal capacitor releases current only at the moment of deployment.

A short to power causes: 1) airbag deployment failure (the power supply bypasses the trigger current); 2) a risk of unintended deployment (if short circuit resistance changes or voltage fluctuates); 3) the SRS system to enter fail-safe mode, disabling all airbag functions.

This fault is a continuous, non-intermittent hard short.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Mechanical wear of the rear seat wiring harness: Long-term chafing between the left rear seat fore-aft slide rail adjustment mechanism and the floor wiring harness damages the yellow airbag wire insulation. The exposed copper core contacts body power wires (such as the seat heating power supply wire or 12V constant live wire), causing a short circuit.
  • 2Connector water ingress and electrolytic corrosion: Water entering the rear footwell, high-pressure car washing, or a blocked A/C drain hose causes water to seep under the seat. Water accumulates between the pins of the airbag wiring harness connector (typically located under the seat or below the C-pillar), forming an electrolytic conductive path and short-circuiting the power and signal terminals.
  • 3Modification damage: Clips, screws, or other fasteners used to install aftermarket full-cover seat covers, leather seats, or rear seat heating pads directly pierce or crush the airbag wiring harness, causing internal wires to short to the power wire.
  • 4Harness securing failure: Original wiring harness retaining clips age and break, causing the harness to sag and contact the seat metal slide rails, brackets, or sharp body edges. Vibration damages the insulation, allowing the harness to contact a live component.
  • 5SRS control module internal fault: Power transistor (IGBT) breakdown or a stuck relay in the control module internal ignition drive circuit causes the circuit terminal to continuously output battery voltage, triggering a false external short circuit detection.
What To Do
  • 1
    Safe power-down and discharge: Turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds (some models require 3 minutes) to fully discharge the SRS control module backup capacitor and prevent accidental airbag deployment.
  • 2
    Removal and visual inspection: Remove the left rear seat assembly (cushion and backrest) and the lower C-pillar trim panel to expose the left rear side airbag module (usually located on the side of the seat backrest or inside the C-pillar trim panel) and wiring harness connector. Inspect the wiring harness insulation for damage, scorch marks, or punctures, and inspect the connector for water ingress, oxidation, or deformed pins.
  • 3
    Circuit isolation measurement: Disconnect the SRS control module main harness connector. Use a multimeter on the resistance setting to measure the resistance between the left rear side airbag circuit pins and power (+B). The normal value is infinite (OL). If the resistance is less than 1Ω, a short to power exists. Next, disconnect the airbag module connector. Measure the harness side and the airbag side separately to determine whether the short is located in the harness or inside the airbag module.
  • 4
    Repair or replace the wiring harness: If the harness is damaged, repair it using layered insulation (inner layer waterproof tape, outer layer heat-shrink tubing) and maintain a clearance of at least 50mm from adjacent power wires. If the harness lies in the seat slide rail travel path, reroute it and install abrasion-resistant corrugated conduit or fabric tape. If the airbag assembly shorts internally (very rare; resistance is 0Ω and the harness is normal), replace the airbag module.
  • 5
    Connector treatment and sealing: If water enters the connector, thoroughly clean the terminals with a precision electrical contact cleaner (not a general-purpose cleaner). Blow dry with compressed air, apply conductive grease, and reconnect. Check the connector waterproof seal and replace if necessary. Secure the connector in a high position with cable ties to prevent future water ingress.
  • 6
    System reset and verification: Restore all connections, reinstall the seat, and connect the battery. Use the BYD dedicated diagnostic tool (VDS2000 or Launch X-431) to clear the fault code. Perform the 'SRS system self-check' or 'ignition circuit resistance learning' and confirm B1742-00 does not recur. Conduct a road test, simulate seat adjustment and bumpy road conditions, and verify fault resolution.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV - Rear seat runner chafed through wiring harness

✓
The airbag warning light would illuminate intermittently while driving, and always after rear passengers adjusted their seat position. Technicians removed the left rear seat and found interference between the seat runner and the airbag wiring harness mounting point. Repeated forward and rearward adjustment had chafed through the insulation of the yellow airbag wire, and the exposed copper contacted the 12V power supply wire for the seat heating module, causing a short to power. Stripping back the harness revealed three wear points, one of which had fused to the red wire.
Original source ↗
BYD DTC AI Analysis

BYD Qin EV450 - Rear connector corroded due to water wading

✓
After driving through standing water (depth up to the lower door sill), the airbag warning light on the instrument panel remained on. The scan tool retrieved code B1742-00. Inspection found obvious mud and water traces inside the white 2-pin airbag connector under the left rear seat. Electrolytic corrosion between the pins formed green oxide, reducing resistance between the power and signal pins to 0.5Ω and causing a short to power.
Original source ↗
BYD DTC AI Analysis

BYD Qin 100 - Aftermarket seat cover damaged wiring harness

✓
After the owner fitted full-surround genuine leather seat covers, the airbag warning light immediately came on and stayed on. Inspection found that metal staples securing the covers had pierced the left rear side airbag wiring harness sheath, causing a short between the airbag igniter wire (yellow) and the seat heater power wire (red). A multimeter reading showed 0Ω resistance to the power supply terminal. After removing the staples and repairing the harness, the fault cleared.
Original source ↗
BYD DTC AI Analysis

BYD Qin 80 - Connector locking tab broke, causing the plug to come loose and short out.

✓
The vehicle operated as a ride-share car. Rear passengers frequently kicked the left rear C-pillar area. Inspection found the left rear side airbag connector locking tab fractured, so the connector did not fully latch. On bumpy roads the connector shifted, the pins contacted the adjacent 12V constant power terminal and caused an intermittent short to power. Replaced the connector and re-secured the wiring harness routing. Problem resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin EV300 - Wiring harness retaining clip aged and detached.

✓
The vehicle is 5 years old. The factory wiring harness retaining clip under the left rear seat had aged and snapped, allowing the harness to sag and contact the seat rail. An aftermarket rear seat heater was installed later; its 12V power cable insulation had worn through and bonded to the OEM airbag harness, causing fault B1742-00. Repair involved reorganising both harnesses, replacing the clip, and separating the high- and low-voltage circuits.
Original source ↗
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.