AU
B175F

DTC B175F indicates the SRS (Supplemental Restraint System) control unit detects the left front curtain airbag (CAB) ignition circuit resistance falls outside the normal range (normal value: 2 — Seal U

Safety System

DTC B175F indicates the SRS (Supplemental Restraint System) control unit detects the left front curtain airbag (CAB) ignition circuit resistance falls outside the normal range (normal value: 2.0–3.0 Ω; fault threshold: >6 Ω or open circuit).

This Level 2 airbag system fault means the affected curtain airbag may fail to deploy or deploy late during a collision, severely compromising occupant side-impact protection.

The SRS ECU continuously monitors each airbag inflator circuit resistance using a Wheatstone bridge.

Excessive resistance typically indicates poor circuit contact, high wiring impedance, or an open circuit within the inflator.

On BYD new energy vehicles, check for potential electromagnetic interference from the high-voltage interlock circuit affecting the SRS.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Poor contact, oxidation, or corrosion at the left front curtain airbag connector (especially the dedicated yellow connector near the B-pillar and C-pillar, where prolonged moisture exposure oxidizes the terminals).
  • 2Airbag wiring harness worn or partially broken (frequent door operation causes fatigue fracture in the roof side rail wiring harness at the hinge, creating a high-resistance connection)
  • 3Internal open circuit in the clock spring (spiral cable) (poor contact in the internal flat ribbon cable if the curtain airbag circuit on this model routes through the clock spring under the steering wheel)
  • 4Open circuit in aged airbag module internal squib (broken bridge wire inside gas generator or cold solder joint)
  • 5SRS control unit internal sampling circuit fault (drift in the ECU internal A/D converter or reference resistor causes a false high resistance reading)
What To Do
  • 1
    Safety preparation: Disconnect the low-voltage battery negative terminal, wait at least 3 minutes (to fully discharge the SRS backup capacitor), wear an anti-static wrist strap, and disable the high-voltage system (perform the high-voltage power-down procedure for new energy vehicles).
  • 2
    Visual inspection: Check the left front side curtain airbag module connector (usually located inside the A-pillar/B-pillar trim) for looseness, water ingress, or corrosion. Check the wiring harness at the door hinge for wear or pinch marks.
  • 3
    Circuit resistance measurement: Disconnect the airbag module connector. Measure the resistance on the wiring harness side using a dedicated airbag tester or a high-precision multimeter (test current <1mA). Normal resistance is <1Ω. If the resistance is too high, measure the circuit in sections to locate the high-resistance point.
  • 4
    Airbag module isolation test: Connect a 2.7Ω dedicated simulator resistor to the circuit in place of the airbag module. If the fault code clears and the resistance is normal, the airbag module is faulty. If the fault persists, continue troubleshooting the wiring harness.
  • 5
    Clock spring inspection (if applicable): If this circuit passes through the steering wheel, inspect the clock spring connector, measure continuity, and replace if necessary.
  • 6
    SRS ECU inspection: If the wiring harness and airbag are normal, check the SRS control unit power supply, ground, and internal faults. Program or replace the SRS ECU if necessary.
  • 7
    Repair and Verification: After repairing the wiring harness or replacing the faulty component, reconnect the battery. Clear the fault code using the BYD dedicated diagnostic tool. Perform an SRS system self-check and confirm B175F does not return and the system status displays normally.
Real-World Cases
BYD DTC AI Analysis

Song MAX B-pillar connector water ingress and oxidation caused high resistance.

✓
A 2019 Song MAX frequently set DTC B175F with intermittent airbag warning light during the rainy season. Inspection found obvious water stains inside the left front side curtain airbag B-pillar connector, with terminals oxidised and black. Aged door seals let rainwater in, causing the connector's waterproof seal to fail. The technician cleaned the terminals, applied conductive protectant, and replaced the waterproof seal to clear the fault.
BYD DTC AI Analysis

Qin Pro roof wiring harness fractured internally at hinge

✓
2020 BYD Qin Pro set B175F at 80,000 km. Airbag module resistance measured normal, but harness circuit resistance was intermittent. Removed the headliner and found the wiring at the left front door upper hinge had fractured internal copper strands from long-term flexing, leaving only partial continuity and creating high resistance. Replaced the damaged harness section, added abrasion protection sleeves, and re-routed the harness to avoid excessive flexing.
BYD DTC AI Analysis

Open circuit in internal squib of side curtain airbag module due to aging

✓
A 2019 Song MAX set DTC B175F after collision repairs. Inspection revealed the left front side curtain airbag had partially deployed but was reset without replacement. Disassembling the module showed infinite resistance at the igniter—the internal bridge wire had broken. We installed a new left front side curtain airbag and performed configuration programming via the diagnostic tool (entering the new airbag serial number). The fault code cleared and the system passed self-test.
BYD DTC AI Analysis

SRS control unit sampling circuit false positive

✓
A Qin gasoline variant still showed DTC B175F after multiple airbag and wiring harness replacements. Oscilloscope testing of the SRS ECU sample voltage waveform revealed abnormal spike interference. Inspection found an aftermarket dashcam installed; its power line was interfering with the SRS system. Removing the device and checking the SRS ECU ground wiring revealed a loose ground point causing reference voltage drift. Tightening the ground point cleared the fault.
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.