AU
B1735

DTC B1735 indicates the airbag control unit (SRS ECU) detects a communication loss or abnormal circuit resistance in the second-row right side airbag module (typically located in the side of the second-row right seat or inside the C-pillar/door trim panel) — Qin Plus

Safety System

DTC B1735 indicates the airbag control unit (SRS ECU) detects a communication loss or abnormal circuit resistance in the second-row right side airbag module (typically located in the side of the second-row right seat or inside the C-pillar/door trim panel).

Specifically, the inflator circuit of this airbag assembly is open (infinite resistance), or the communication line between the module and the SRS ECU is open.

This is an active safety system fault.

During a side collision, this airbag may fail to deploy, leaving the second-row right occupant without side impact protection.

Disconnected physical connections, damaged wiring harnesses, an open inflator inside the airbag module, or poor terminal contact at the SRS ECU typically cause this fault.

Use the dedicated diagnostic tool (VDS2000/VDS3000) and the wiring diagram to pinpoint the fault.

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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Yellow dedicated wiring harness connector under the seat or at the B-pillar loose, disconnected, or locking tab not fully engaged (commonly caused by frequent fore-and-aft second-row seat adjustments or passenger kicks).
  • 2Right middle-row side airbag module internal igniter open circuit or module communication circuit fault (airbag assembly damaged)
  • 3The wiring harness connecting the airbag module to the SRS ECU is chafed or broken, or the seat rails pinched or sheared the harness over time, fracturing the copper wires.
  • 4Water ingress or improper interior cleaning oxidises or corrodes connector terminals, causing excessive contact resistance (>3Ω) that registers as an open circuit.
  • 5Failure to correctly reconnect the airbag wiring harness after recent seat removal/installation, interior trim modification, or accident repairs, or failure to lock the connector with an audible "click".
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the 12V battery negative terminal, and wait at least 90 seconds (allowing the SRS backup power capacitor to discharge fully). Never use a standard multimeter to directly measure the airbag squib resistance, as this may trigger accidental deployment.
  • 2
    Visual inspection: Remove the second-row right seat side trim panel or lower C-pillar trim panel. Verify the yellow dedicated airbag module connector (typically equipped with a double-locking mechanism) is fully seated. Confirm the locking tab (CPA) is in the locked position, free of looseness or terminal back-out.
  • 3
    Wiring harness physical inspection: Inspect the wiring harness routing from the airbag module to the SRS ECU. Check the corrugated protective conduit near the seat rails and B-pillar hinge area for damage. Look for signs of the seat track crushing or shearing the harness.
  • 4
    Resistance and continuity test: Use a dedicated airbag system diagnostic tool (or a multimeter with a low-current test function) to measure the right middle-row side airbag circuit resistance at the SRS ECU connector. The standard value is typically 2.0-3.0 ohms. Infinite resistance (∞) indicates an open circuit in the wiring or module; resistance <1 ohm indicates a possible short circuit. Simultaneously measure the wiring harness insulation resistance to ground and to power; the value must be >1 MΩ.
  • 5
    Segmented isolation diagnosis: Disconnect the airbag module connector. Use a jumper wire to short the two terminals on the ECU-side wiring harness. If the fault code changes to "resistance too low", the wiring harness is normal and the fault lies in the airbag module itself. If the code still reads "not connected", the fault lies in the wiring harness or the ECU.
  • 6
    Component replacement and verification: If the airbag module is faulty, replace the right middle-row side airbag assembly. If the wiring harness is faulty, repair or replace the wiring harness. After repair, reconnect the battery. Use the VDS diagnostic tool to clear the fault code. Perform the 'SRS system self-check' and 'crash sensor calibration' (if required). Verify B1735 does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

2019 Song MAX reports B1735 fault after frequent seat adjustments

✓
The owner of a Song MAX with 30,000 km reported the airbag warning light on the instrument panel was constantly on. VDS retrieved DTC B1735 (right middle-row side airbag not connected). Inspection found the right-hand second-row seat adjusted to the foremost position. The yellow airbag connector lock tab under the seat had detached, and the plug was loose by about 5 mm. The owner frequently moved the seat for child pick-ups; the rail movement pulled on the wiring harness. Reconnected the connector firmly, reinstalled the lock tab, and secured the wiring harness with cable ties to keep it clear of the seat rail. Resolved the fault.
BYD DTC AI Analysis

2021 Tang DM airbag warning light on after accident repair

✓
Minor scrape on right rear side. After a third-party repair shop replaced the right rear door and C-pillar trim panel, the dashboard displayed an airbag fault. The diagnostic scanner showed code B1735. Inspection found the technician had trapped the right second-row side airbag wiring harness connector beneath the trim panel clip during installation, leaving the connector partially disconnected and the pins bent. Straightened the pins and rerouted the wiring to ensure the connector fully locked. Fault resolved.
BYD DTC AI Analysis

2019 BYD Yuan EV: Airbag system warning after wading through water

✓
After the vehicle was driven through heavy rain and floodwater (water level up to the middle of the doors), the instrument cluster displayed an airbag fault. Retrieved fault codes included B1735. Removed the second-row right-side seat and carpet, and found clear water stains and copper oxidation inside the airbag wiring harness connector. The cause: deteriorated door seals allowed rainwater to enter and pool at the lowest point of the harness under the seat. Cleaned the oxidised terminals, applied a special conductive anti-corrosion compound, replaced the door seals, and dried the harness. Fault resolved.
BYD DTC AI Analysis

2020 Qin Pro airbag module internal open circuit

✓
No accident history. Airbag warning light came on intermittently, especially during cold starts. DTC B1735 appeared intermittently. Checked harness connections: normal; measured harness continuity: good. Suspected a cold solder joint or poor connection in the igniter or flexible circuit board inside the airbag module. After disconnecting the battery and allowing sufficient time, substituted a known-good airbag module for testing; fault did not reappear. Replaced the right middle row side airbag assembly (part number must match vehicle configuration). Fault completely resolved.
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.