AU
B170D

DTC B170D indicates the SRS (Supplemental Restraint System) control unit detects an open circuit or disconnection in the right-hand (RH) curtain airbag circuit — Seal U

Safety System

DTC B170D indicates the SRS (Supplemental Restraint System) control unit detects an open circuit or disconnection in the right-hand (RH) curtain airbag circuit.

Specifically, during the self-test, the control unit fails to detect the load signal from the RH curtain airbag inflator within the specified time (typically under 6 seconds).

Normal resistance is 1.6-2.4Ω.

This fault prevents the RH curtain airbag from deploying during a side impact or rollover accident, severely compromising occupant head protection, and continuously illuminates the instrument panel SRS warning light.

Determine whether the cause is a loose harness connector, an open circuit in the wiring, or a faulty curtain airbag module.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Curtain airbag wiring harness connector (usually a yellow or white 2-pin connector) not fully locked or terminal backed out after removing and installing the right A-pillar or C-pillar interior trim panel. This commonly occurs after vehicle window tinting, audio modifications, or accident repairs.
  • 2Roof wiring harness retaining clip failure causes the harness to rub against a sharp body edge during driving vibrations, resulting in an open circuit. Commonly seen on Yuan and Song MAX models.
  • 3Moisture intrusion into the connector during vehicle wading or high-pressure washing oxidizes and corrodes the copper pins, resulting in high resistance or an open circuit.
  • 4Internal open circuit in the right-side curtain airbag module (gas generator), typically associated with a vehicle accident history or the module exceeding its service life.
  • 5SRS control unit internal detection circuit fault (very rare; consider only after ruling out wiring faults)
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 2
    Fault status confirmation: Use VDS2000 or a dedicated BYD diagnostic tool to read the fault code. Confirm B170D is a current fault (Active), not a historical fault (History), and record the freeze frame data.
  • 3
    Visual inspection: Remove the right A-pillar upper trim panel, roof grab handle, and sun visor. Inspect the curtain airbag wiring harness corrugated conduit along the roof side rail for damage. Specifically check the curtain airbag connectors at the upper A-pillar and C-pillar for looseness, water ingress, or backed-out terminals.
  • 4
    Resistance measurement: Disconnect the curtain airbag connector. Use a digital multimeter to measure the resistance on the curtain airbag module side. Normal value: 1.6-2.4 Ω. Measure the resistance between the wiring harness side and body ground (must be greater than 10 MΩ to confirm no short to ground). Measure the voltage on the wiring harness side (must be less than 1 V to confirm no short to power).
  • 5
    Wiring repair: If the wiring harness has an open circuit, solder the repair and wrap it with two layers of high-temperature insulating tape. Re-secure the wiring harness to prevent contact with sharp sheet metal edges. If the connector is corroded, clean it with electrical contact cleaner, apply conductive grease, and fully engage the connector secondary lock (CPA).
  • 6
    System verification: Restore all connections. Turn on the power. Clear the fault codes. Turn the ignition switch to the ON position and wait 6 seconds. Confirm the instrument cluster SRS warning light turns off after completing its self-check. Perform a right side impact sensor simulation test (use the diagnostic tool to perform an active test) to confirm the curtain airbag circuit communication is normal.
Real-World Cases
BYD DTC AI Analysis

Song MAX right side curtain airbag intermittently sets fault code after accident repair

✓
Vehicle: 2019 BYD Song MAX, 32,000 km. Symptoms: SRS warning light intermittently illuminated after accident repair. Retrieved DTC B170D (right curtain airbag not connected). Cleared the code, but it returned after one week. Diagnosis: Removed the right A-pillar trim and found the curtain airbag connector was not fully inserted during the accident repair. The secondary locking tab was not engaged, allowing vehicle vibration to work the connector loose. Repair: Re-seated the connector, confirmed the CPA (Connector Position Assurance) lock was fully engaged, and secured the wiring harness with cable ties. One-week follow-up: fault has not recurred.
BYD DTC AI Analysis

Tang DM right side curtain airbag circuit corroded open after wading

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Vehicle: 2021 Tang DM, 58,000 km. Symptoms: SRS warning light stayed on constantly after driving through floodwater during a typhoon, with active DTC B170D. Diagnosis: Inspected the right curtain airbag connector (inside the right front door frame upper trim panel). Found significant water ingress and green copper corrosion inside the connector. Pin oxidation caused contact resistance to exceed 10 Ω (normal <2 Ω). Repair: Replaced the curtain airbag wiring harness connector (part number: verify against vehicle configuration). Cleaned the curtain airbag module pins thoroughly with electronic contact cleaner, dried, applied conductive grease, and re-sealed the connector against water intrusion. Cleared DTCs; system normal.
BYD DTC AI Analysis

Yuan EV side curtain airbag false alarm after window tinting

✓
Vehicle: 2019 BYD Yuan EV535, 11,000 km. Symptoms: SRS warning light came on the day after windscreen tinting, storing DTC B170D. Diagnosis: The owner reported the right A-pillar trim had been removed during tinting. Inspection found that a trim clip pinched the curtain airbag wiring harness when the panel was reinstalled, deforming the connector terminal and causing the pin to back out, creating an open circuit. Repair: Straightened the deformed pin, rerouted the wiring harness to prevent interference with the trim clips, and rewrapped the corrugated tubing. Cleared the fault code and ran an SRS self-test – passed.
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.