AU
B175E

DTC B175E indicates the Left Front Side Curtain Airbag ignition circuit resistance is below the normal threshold established by the SRS control unit (ACU) (typically 1 — Seal U

Safety System

DTC B175E indicates the Left Front Side Curtain Airbag ignition circuit resistance is below the normal threshold established by the SRS control unit (ACU) (typically 1.0–3.0 Ω, depending on model year).

Low resistance indicates a short circuit, either complete (near 0 Ω) or partial.

This fault causes the SRS system to flag the circuit as abnormal.

During a collision, the airbag may fail to deploy or may deploy unintentionally.

Consequently, the ACU illuminates the airbag warning light, stores the fault code, and may disable the entire airbag system to protect occupants.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Airbag wiring harness wear or compression shorts the positive and negative wires: The side curtain airbag wiring harness runs along the A-pillar and roof side rail. Long-term vibration may damage the harness insulation, especially near the door hinges or harness retaining clips.
  • 2Airbag connector water ingress or terminal corrosion: The left front side curtain airbag connector is located below the A-pillar or inside the sill trim. Car washing, wading, or poor sealing allows water ingress, causing a short circuit between terminals or reduced resistance.
  • 3Side curtain airbag inflator internal short circuit: An internal short in the igniter bridge wire or damp propellant causes an abnormal drop in resistance, indicating a fault in the airbag assembly.
  • 4SRS control unit (ACU) internal detection circuit fault: Faulty ACU internal sampling resistor or detection chip causes a false low resistance reading.
  • 5Improper modification or repair: excessively long fixing screws piercing the wiring harness during dash cam installation or headliner removal and installation, or trim panel clips pinching an improperly secured wiring harness.
What To Do
  • 1
    Safe power-down and wait: Turn off the ignition switch, disconnect the battery negative terminal, and wait at least 90 seconds (to ensure the SRS capacitor fully discharges). Do not measure the airbag circuit while powered on.
  • 2
    Read freeze frame and data stream: Connect the diagnostic tool to read the B175E freeze frame data. Record information such as vehicle speed and temperature when the fault occurred. Read the SRS data stream to check the real-time resistance of the left front side curtain airbag (normal: approx. 2.0-3.0Ω; faulty: typically <1.0Ω or displays 0.0Ω).
  • 3
    Isolate the fault by disconnecting the airbag connector: Remove the lower A-pillar trim panel and locate the left front curtain airbag connector (usually has a yellow shorting clip). Disconnect the connector and use a dedicated probe to measure the resistance at the airbag unit side (must be within 2.0 ± 0.5 Ω). If the resistance is normal, the fault is in the wiring harness or ECU. If the resistance remains low, replace the airbag assembly.
  • 4
    Harness continuity and insulation check: Measure resistance between the harness-side connector pins (should be >10kΩ, open circuit). Measure insulation resistance from each pin to ground and power (should be >1MΩ). Focus inspection on the harness bend inside the A-pillar and contact points between the roof harness and body metal.
  • 5
    Connector terminal inspection: Inspect connector pins for oxidation, deformation, or looseness. Check the shorting bar (SST) for failure causing a normally closed short circuit. Clean the terminals and apply specified conductive grease. Replace the connector if necessary.
  • 6
    SRS ECU verification: If the wiring harness and airbag unit are normal, install a known-good ACU to test for an internal control unit fault. After repair, clear the fault code and perform a system self-check (the indicator lamp should turn off).
Real-World Cases
BYD DTC AI Analysis

Song MAX side curtain airbag shorted after water wading

✓
2019 BYD Song MAX, 30,000 km. After wading through heavy floodwater, the airbag warning light stayed on constantly. Read DTC B175E (left front side curtain airbag resistance too low). Live data showed 0.3Ω. Removed the trim below the left A-pillar and found visible water inside the airbag connector. Terminal oxidation caused a short. Cleaned the terminals with electronic contact cleaner, dried them, and applied conductive grease. Resistance returned to normal at 2.2Ω and the fault cleared. Check the door seals and A-pillar waterproof membrane.
BYD DTC AI Analysis

Modified wiring harness crushed on Qin Pro, causing short circuit

✓
2020 BYD Qin (petrol variant). DTC B175E set one week after installing an aftermarket panoramic sunroof ambient lighting kit. Removed the headliner and found the aftermarket wiring harness retaining clips were too long, pinching the left front side curtain airbag harness and damaging the insulation. The exposed copper core shorted to ground against the body. Repaired the harness with insulating tape and heat-shrink tubing, rerouted it to avoid sharp components. Cleared the DTC; it has not returned. Note: Avoid OEM airbag wiring channels when modifying.
BYD DTC AI Analysis

Side curtain airbag inflator internal fault

✓
2019 Song MAX, no collision history. Parked overnight; airbag warning light illuminated on startup. Scanner showed DTC B175E. Disconnected the airbag connector: wiring harness side measured infinite resistance (normal), airbag side measured 0.1Ω (internal short). Replaced the left front side curtain airbag assembly (including gas generator). Fault cleared. Root cause: gas generator internal bridge wire insulation breakdown from aging—component quality defect. Recommend warranty claim.
BYD DTC AI Analysis

A-pillar wiring harness chafed, causing intermittent short circuit

✓
2019 BYD Song MAX. Airbag warning light occasionally illuminated while driving and cleared on restart. DTC B175E (intermittent). Removed left A-pillar trim and inspected the harness; found insulation chafed through at the mounting clip due to repeated door opening and closing. The harness compressed against the clip when the door closed, causing intermittent shorts. Static resistance was normal but dropped below 0.5Ω when wiggling the harness. Replaced the damaged section, added an abrasion-resistant sleeve, and rerouted the harness with adequate slack. Fault completely resolved.
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.