AU
B1732

DTC B1732 indicates the Airbag Control Unit (ACU) detects the Left Middle Row Side Airbag Module squib circuit resistance falls outside the manufacturer's normal threshold (BYD standard is typically 1 — Seal U

Safety System

DTC B1732 indicates the Airbag Control Unit (ACU) detects the Left Middle Row Side Airbag Module squib circuit resistance falls outside the manufacturer's normal threshold (BYD standard is typically 1.6-2.0Ω, with a ±0.3Ω tolerance). "Resistance too high" usually means the resistance exceeds the upper limit (e.g., >2.5Ω or approaching an open circuit), indicating a high-impedance connection in the circuit.

Connector oxidation, poor wiring harness connections, an internal open circuit in the airbag module, or increased partial winding resistance can cause this condition.

Essentially, the SRS self-check detects reduced reliability in the secondary protection circuit.

This condition can prevent the airbag from deploying fully within the specified time (typically <10ms) or with sufficient energy during a side-impact collision, degrading or disabling side-impact protection for the left middle-row occupant.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose, backed-out, or oxidized/corroded airbag wiring harness connector under the left middle-row seat (usually near the seat rail or inside the lower C-pillar trim panel), especially common after vehicle wading or interior cleaning.
  • 2Poor contact, partially broken copper strands, or pinched or deformed wiring in the harness between the airbag module and the ACU (commonly at bends caused by frequent fore-and-aft seat adjustment, or at the body-to-seat connector)
  • 3Increased igniter resistance inside the left middle row side airbag module (generator winding aging, oxidized internal solder joints, or micro-open circuit), indicating end-of-life component failure.
  • 4Airbag control unit (ACU) internal detection circuit or sampling resistor fault causing a false code (rule out via cross-checking)
  • 5Airbag wiring harness crushed, punctured, or not torqued to specification during vehicle modification or repair, causing a hidden open circuit.
What To Do
  • 1
    Safety preparation: Turn the ignition switch to OFF, disconnect the negative battery terminal, wait at least 90 seconds (to ensure the SRS capacitor fully discharges), and wear an anti-static wrist strap.
  • 2
    Fault confirmation: Use a BYD VDS2000 or equivalent diagnostic tool to read the freeze frame data. Record the ambient temperature and voltage at the time of the fault. Confirm whether the fault is 'Active' or 'Stored'.
  • 3
    Visual inspection: Remove the left middle-row seat side trim panel or lower C-pillar trim panel. Locate the airbag module (white connector, usually with yellow markings). Verify the connector is fully locked. Inspect the pins for blue-green oxidation, burning, or back-out.
  • 4
    Resistance measurement: Disconnect the airbag module connector. Use a digital multimeter (accuracy 0.1Ω) to measure the resistance between the two airbag module terminals. Standard value: 1.5-2.5Ω. If the resistance is >3.0Ω or reads 'OL' (open circuit), the module itself is faulty.
  • 5
    Wiring harness check: Connect an airbag simulator (2Ω load) in place of the airbag module. If the fault code changes to "normal resistance", the wiring harness is normal and the fault is in the airbag module. If the system still reports high resistance, measure the wiring harness continuity between the connector and the ACU (should be <1Ω) and the insulation to ground/power (should be >1MΩ).
  • 6
    Key inspection areas: Inspect the mating connector between the floor wiring harness and the seat wiring harness (usually under the carpet beneath the seat) and the wiring harness inside the rubber grommet at the body pass-through hole for breaks, water stains, or wear.
  • 7
    Repair action: If oxidation is present, clean with precision electronic contact cleaner and apply conductive grease; if the wiring harness is broken, repair using solder and heat-shrink tubing, or replace the wiring harness assembly; if the airbag module is faulty, replace with an airbag module of the same model (Note: Disconnect the battery before operation).
  • 8
    Verification test: Restore all connections, connect the battery, and turn the ignition switch to ON. Use the diagnostic tool to clear the fault code and perform the 'SRS system self-test'. Confirm B1732 does not return. Verify the airbag warning light turns off after 6 seconds.
Real-World Cases
BYD DTC AI Analysis

Water ingress and oxidation of connector under left second-row seat on Song MAX.

✓
My 2019 BYD Song MAX (30,000 km) had the airbag light stay on after rain. I pulled DTC B1732. Under the left second-row seat, the yellow airbag harness connector seal had perished, letting water in and causing oxidation on the copper pins. I measured contact resistance at 4.2 ohms. The fix: cleaned the pins with WD-40 precision electrical cleaner, lightly sanded the oxidation with 1000-grit sandpaper, re-crimped the pins, replaced the waterproof seal, applied conductive silicone grease, and put everything back. Resistance dropped to 1.8 ohms – fault cleared.
BYD DTC AI Analysis

Tang DM left second-row side airbag wiring harness chafed, causing intermittent connection.

✓
2021 BYD Tang DM. The airbag warning light illuminated intermittently, particularly on rough roads. Scan tool showed B1732 as an intermittent fault. Removed and inspected the left C-pillar trim and found the side airbag harness rubber grommet had come off where it passes through the body panel hole, leaving the harness to rub against the metal edge. Internal copper strands were partially broken; only 3–4 strands remained connected, causing high resistance (measured 8.5 Ω). Replaced the complete harness section from the floor harness to the airbag module, including the grommet. Re-secured the harness routing to avoid contact with hard objects. Fault fully resolved.
BYD DTC AI Analysis

Yuan EV left second-row side airbag module deteriorated

✓
2019 BYD Yuan EV, five years old. No collision history, but the airbag warning light illuminated with DTC B1732. Disconnected the airbag module connector and directly measured the module's internal resistance: 3.9Ω (exceeds upper standard limit). Checked the wiring harness — normal, good ground insulation. Diagnosed the issue as the airbag igniter winding degrading over time, causing resistance to gradually increase. Resolution: Ordered a replacement left second-row side airbag module with the same part number (verify the vehicle has second-row side airbags). Following the workshop manual, disconnected the battery, removed the seat, and replaced the module. Inspected the connector for abnormalities before installing the new module. After replacement, the fault code cleared and has not returned.
BYD DTC AI Analysis

Qin Pro seat adjustment caused the connector to come loose.

✓
2020 BYD Qin Pro. The left rear seat is manually adjustable; the owner reported the SRS warning light illuminated after adjusting the seat. Inspection found the airbag harness connector above the seat sliding rail was not fully seated (locking tab not engaged), gradually working loose during fore-aft movement and causing poor pin contact with resistance fluctuating between 1.8 and 5.6 Ω. Repair: Reconnected the connector and ensured an audible click from the locking tab, then secured the harness to the seat frame with cable ties, leaving enough slack for full seat travel without straining the connection, to prevent recurrence.
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.