AU
B175B

DTC B175B indicates the Airbag Control Unit (ACU) detects the igniter (squib) circuit resistance for the right rear side airbag (typically the right C-pillar curtain airbag or right rear seat side airbag) falls below the system threshold (generally <1 — Seal U

Safety System

DTC B175B indicates the Airbag Control Unit (ACU) detects the igniter (squib) circuit resistance for the right rear side airbag (typically the right C-pillar curtain airbag or right rear seat side airbag) falls below the system threshold (generally <1.5 Ω).

Normal airbag igniter resistance is 2.0-3.0 Ω.

Low resistance indicates a circuit short to ground, a wire-to-wire short, or an internal short within the airbag module igniter.

The ACU consequently registers the airbag as deployed or the circuit as faulty, disabling the airbag deployment function.

During a side impact, the right rear side airbag fails to inflate and protect the occupant.

This condition may trigger a continuous airbag warning lamp and constitutes a critical fault compromising passive safety.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wear or pinching of the right rear side airbag wiring harness damages the insulation, causing a short to ground (commonly results from improper C-pillar trim panel removal/installation or the seat slide rail crushing the wiring).
  • 2Water ingress, oxidation, or deformed pins in the airbag wiring harness connector (usually located inside the right rear door sill trim panel or below the C-pillar), causing a short circuit between terminals.
  • 3Airbag gas generator (igniter) internal short circuit failure, permanently low resistance.
  • 4Airbag Control Unit (ACU) internal sampling circuit fault or software false alarm
  • 5Poor sealing of the right rear wiring harness connector allows moisture intrusion after driving the vehicle through water or deep cleaning the interior.
What To Do
  • 1
    Use the BYD VDS2000 or ED400 diagnostic tool to read the fault code, confirm B175B is active, record freeze frame data, and check the specific resistance value in the data stream (typically <1.0Ω).
  • 2
    Disconnect the battery negative terminal and wait at least 3 minutes for the SRS capacitor to fully discharge to prevent accidental airbag deployment.
  • 3
    Remove the right C-pillar trim panel or right rear seat (depending on vehicle configuration). Locate the right rear side airbag wiring harness connector (black or yellow dedicated plug). Inspect the connector for water ingress, corrosion, or looseness.
  • 4
    Disconnect the airbag module connector and use a dedicated airbag resistance tester (or a 2.7Ω safety resistor connected in series) to measure the resistance of the airbag assembly. If the resistance is <1.5Ω, this indicates an internal short circuit in the airbag assembly. Replace the airbag module.
  • 5
    If the airbag unit is normal, use a multimeter to measure the resistance between the harness-side connector and body ground. The resistance should be infinite. If continuity exists, inspect the harness along its routing for wear points. Focus on movement interference areas where the harness passes door seals and seat mounting brackets.
  • 6
    Check the Airbag Control Unit (ACU) terminal pins for bending or backing out. Measure continuity from the wiring harness end to the ACU end; resistance should be <1Ω.
  • 7
    Repair damaged wiring harness sections (use heat-shrink tubing or replace the harness). Service connectors with water ingress (clean, blow dry, and apply conductive grease). Replace the entire airbag wiring harness if necessary.
  • 8
    Reconnect all connectors and ensure the locking tabs are fully engaged. Reconnect the battery. Use the diagnostic tool to clear the fault code. Perform the 'SRS system self-check' function and confirm B175B does not return.
  • 9
    Perform a road test to simulate vehicle vibration and observe if the fault recurs. Finally, use the diagnostic tool to view the data stream and confirm the right rear side airbag resistance value has returned to the normal range of 2.0-3.0Ω.
Real-World Cases
BYD DTC AI Analysis

Seat mounting bolt crushed right rear curtain airbag wiring harness on Song MAX, causing short circuit

✓
A 2019 BYD Song MAX with 30,000 km arrived with the airbag warning light on. Scanning retrieved DTC B175B. Removing the right rear C-pillar trim revealed the side curtain airbag harness routed incorrectly at the seat mounting bracket; the seat mounting bolt had compressed the wiring over time, damaging the insulation and exposing the copper to the body ground. Repair: Cut out the damaged section, soldered in an extension wire, and sealed it with double-walled heat-shrink tubing. Rerouted the harness to clear the interference point. Fault resolved.
BYD DTC AI Analysis

Tang DM right rear airbag connector corrosion due to water ingress after wading

✓
2021 Tang DM. Airbag warning light appeared the day after driving through floodwater. Scanner showed active fault code B175B. Inspected the airbag connector inside the right rear sill trim panel and found the seal had deteriorated. Water ingress during wading caused terminal oxidation with green copper corrosion, creating a short between the pins. Replaced the airbag wiring harness connector (with waterproof seal), cleaned the airbag module terminals, and applied waterproof silicone grease to the connection. Fault resolved.
BYD DTC AI Analysis

Abnormal airbag resistance after accident repair on Yuan EV

✓
2019 BYD Yuan EV, right rear side collision. After an external workshop replaced the right rear side airbag, the instrument cluster displayed an airbag warning and set DTC B175B. Inspection revealed the technician had installed an aftermarket airbag assembly with an igniter resistance of only 0.8Ω, below the BYD ACU recognition threshold. Replaced the assembly with a genuine BYD right rear side airbag (part number must match VIN), executed 'Configuration Code Write' and 'Airbag Deployment Verification' using a diagnostic tool, and cleared the fault code.
BYD DTC AI Analysis

BYD Qin Pro: Frequent right rear seat adjustment caused wiring harness fatigue fracture and short circuit

✓
2020 Qin petrol variant. The right rear seat has a 60/40 split-fold design; the owner frequently folded the seat to transport cargo. Long-term flexing caused the airbag wiring harness inside the seat to fatigue and fracture. The exposed copper wires at the break splayed out and contacted the seat frame, shorting the circuit and setting DTC B175B. Repair action: Replaced the right rear seat airbag wiring harness assembly (including protective convoluted tubing). Added wiring harness retaining clips at the flex point to limit movement. Instructed the owner on proper use of the seat folding function.
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.