AU
B170F

DTC B170F indicates a short to power (B+) in the right-hand curtain airbag (SRS Curtain Shield Airbag - RH) ignition circuit — Seal U

Safety System

DTC B170F indicates a short to power (B+) in the right-hand curtain airbag (SRS Curtain Shield Airbag - RH) ignition circuit.

In the BYD SRS system, the curtain airbag uses an electrically ignited gas generator.

During normal operation, the control unit supplies a momentary high current to trigger ignition.

The diagnostic system triggers this fault when it detects abnormal continuity (resistance below the threshold, typically <10Ω) between the curtain airbag ignition circuit and the vehicle power supply (12V battery positive terminal), or when the circuit voltage remains above the set value (approximately 5V).

This is a hard fault.

The SRS control unit immediately disables the right-hand curtain airbag function and illuminates the instrument cluster airbag warning lamp.

Potential risks include: 1) The right-hand curtain airbag fails to deploy in a collision, resulting in a loss of occupant head protection. 2) In extreme cases, if the short circuit contact resistance fluctuates, vehicle jolts can generate a momentary current, creating a minimal risk of unintended curtain airbag deployment.

Therefore, the system classifies this as a severe fault and prohibits continued vehicle operation.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness insulation wear inside the right A-pillar or C-pillar trim panel: During long-term vehicle use, the right roof curtain airbag wiring harness rubs against sharp metal body edges (such as the roof crossmember mounting bracket). This friction damages the insulation between the positive and negative wires or between the power and ignition wires, causing a short circuit to the constant power wire.
  • 2Curtain airbag connector water ingress and oxidation: A blocked sunroof drain tube or poor sealing allows rainwater to seep into the right headliner. Water accumulates between the pins of the curtain airbag connector (usually located at the right D-pillar or right side of the headliner). The electrolyte forms a conductive path, causing a power short circuit.
  • 3Incorrect wiring connection after accident repair: Following a right-side collision or roof trim removal and installation, technicians mistakenly connected the curtain airbag ignition wire (normally a high-resistance circuit) to a constant power wire (such as the reading light or sun visor light power supply), or missing harness retaining clips caused the harness to shift and contact a power source.
  • 4Damaged internal driver chip in the SRS control unit: Breakdown of the internal ignition driver transistor (IGBT) or a logic circuit fault causes a false short-to-power detection in the curtain airbag circuit, or internal power supply filter capacitor leakage causes an abnormal reference voltage.
  • 5Aftermarket modification damage: When installing a dash cam, headliner ambient lighting, or an aftermarket sunroof, fixing screws or harness clips pierce the right curtain airbag harness insulation, causing a short circuit to the vehicle power harness (such as the headliner lighting circuit).
What To Do
  • 1
    Safety pre-check and fault confirmation: Use the VDS2000/3000 diagnostic tool to read all SRS fault codes. Confirm B170F is a current fault (Present), not a history fault (History). Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS backup power supply and prevent accidental airbag deployment.
  • 2
    Right curtain airbag wiring harness visual inspection: Remove the right A-pillar, B-pillar, and C-pillar interior trim panels, and the right headliner trim panel. Inspect the orange curtain airbag module wiring harness (usually marked RCurtain or R CSA) along the roof side rail (standard BYD SRS wiring harnesses are orange or yellow). Check for detached harness retaining clips, worn insulation, and water stains or corrosion on the connectors.
  • 3
    Circuit isolation test: Disconnect the 2-way connector between the SRS control unit and the right curtain airbag module. Use a multimeter to measure the resistance from the curtain airbag side wiring harness to body ground and the 12V power supply. The normal reading is infinity (OL). If the multimeter indicates continuity or resistance <10 kΩ, the wiring harness is shorted to power. Locate the short circuit.
  • 4
    Harness routing localization: Use a sectional inspection method. Start from the curtain airbag module and work toward the control unit. Progressively peel back the corrugated conduit and check the harness insulation where it passes through body sheet metal holes, runs past the seat mounting bracket, and approaches the roof light socket. Monitor the circuit voltage with an oscilloscope to check for abnormal 12V voltage.
  • 5
    Component inspection: Disconnect the curtain airbag module connector. Measure the resistance between the two curtain airbag inflator terminals, and between each terminal and the housing. The normal value is 2.0-3.0 Ω (BYD standard). If the resistance is 0 Ω or ∞, or if either terminal has continuity with the vehicle body, this indicates an internal short circuit in the curtain airbag. Replace the right curtain airbag assembly.
  • 6
    Control unit verification: If the wiring harness test is normal, short the curtain airbag circuit measurement points on the SRS control unit side and use the diagnostic tool to perform the 'Ignition Circuit Self-test'. If it still reports a short to power, the SRS ECU has an internal fault. Replace the control unit and perform coding matching.
  • 7
    Repair and Replacement: Repair the damaged wiring harness using a double layer of high-temperature insulating tape and heat-shrink tubing (rated withstand voltage >500V), or replace the curtain airbag module. Do not simply wrap the harness with tape; use a dedicated automotive wiring harness repair kit. When replacing the curtain airbag, record the inflator serial number and synchronize it to the diagnostic tool.
  • 8
    System reset and verification: Reconnect all connectors and the battery, then clear the fault codes. Perform 'SRS system initialisation' (coding match) and 'ignition circuit resistance learning'. Perform three key cycles (OFF-ON). Confirm the instrument cluster airbag warning lamp turns off and the diagnostic tool displays no current fault codes. Finally, perform a right curtain airbag simulated deployment test (using the dedicated load tool, not a live deployment) to verify the circuit resistance is within the normal range.
Real-World Cases
BYD DTC AI Analysis

Repaired right-side curtain airbag short circuit after wading in Song Pro DM

✓
2020 BYD Song Pro DM. After heavy rain, the instrument cluster displayed 'Please Check SRS System'. Diagnostic tool reported DTC B170F. Inspection found the sunroof drain hose blocked. Rainwater flowed down the right A‑pillar into the curtain airbag connector located inside the headliner above the right front seat, causing electrolytic corrosion between the pins that created a conductive bridge. Removed the right side headliner and found green oxide deposits inside the connector. Repair: Replaced the right curtain airbag wiring harness assembly (including connector), cleared the sunroof drain hose, applied waterproof silicone grease to the curtain airbag connector, and fitted a waterproof cover. After repair, a 30‑minute simulated water spray test using compressed air confirmed no recurrence.
BYD DTC AI Analysis

Misconnected wiring harness after accident repair on Tang EV caused curtain airbag power supply short circuit

✓
2021 Tang EV. DTC B170F appeared one week after right-side accident repairs. The repair history showed the right-side headliner had been replaced. Inspection found that during the accident repair at the dealership, the right curtain airbag harness (orange) and headliner reading lamp power wire (white) were incorrectly inserted into the same pin at the B-pillar connector, causing the airbag circuit to connect directly to 12V constant power. Further inspection revealed missing harness retaining clips, and harness movement accelerated wear. Resolution: Rerouted the harness, replaced the damaged curtain airbag igniter harness section (from B-pillar to airbag module), restored correct wiring, and installed the missing retaining clips. Wrapped the harness with specialized harness tape (TESA 51036) for protection.
BYD DTC AI Analysis

Aftermarket panoramic sunroof retrofit on Yuan EV causing curtain airbag fault

✓
2019 BYD Yuan EV. Owner fitted a panoramic sunroof at an auto accessory market. The next day, a B170F fault code appeared, accompanied by headliner noise. Inspection found the installer used over-long self-tapping screws to secure the sunroof frame, which pierced the right curtain airbag harness (at the right roof rail). This shorted the curtain airbag igniter (+) wire to the sunroof motor’s constant 12V supply. Repair: Due to the extended short-circuit duration, the curtain airbag module may have sustained internal damage. Replaced the right curtain airbag assembly (P/N: MEF-5856020). Repaired the damaged harness by recrimping with Delphi 15304720 waterproof terminals and insulating with double-layer heat shrink tubing. Advised the owner to revert to the original sunroof configuration to avoid safety system risks.
BYD DTC AI Analysis

BYD Qin Pro (Petrol): SRS control unit false fault

✓
2020 BYD Qin Pro, no accident or modification history. Intermittent B170F DTC; sometimes reappears after clearing and driving 100 km. Wiring harness insulation: good. Curtain airbag resistance: 2.3 Ω (normal). No short to power in wiring. Oscilloscope monitoring revealed instantaneous high-voltage spikes (>20 V) at the SRS control unit ignition driver terminal when driving on rough roads. Determined faulty internal voltage regulation circuit in SRS control unit, causing false short-to-power detection. Solution: Replaced SRS control unit (P/N: ECU-3636100), performed online coding (VIN match) and sensor calibration. Executed 'Crash Record Clear' and 'System Configuration Write' with diagnostic tool. Fault resolved.
BYD DTC AI Analysis

Song MAX headlining incorrectly fitted, chafing wiring harness

✓
2019 Song MAX, 30,000 km. Intermittent DTC B170F appeared, especially after high summer temperatures. Inspection found a fractured right-side headliner trim panel clip. The failed clip allowed the trim to sag and compress the curtain airbag harness. The harness chafed against the sharp edge of the roof crossbeam, damaging the insulation and exposing the copper wire. The exposed wire contacted the interior light power wire. Repair: Replaced the right curtain airbag harness (A-pillar to C-pillar section). Replaced all headliner plastic clips with improved metal-reinforced clips. Installed rubber grommets where the harness passes through sheet metal holes. Rerouted the harness to avoid contact with sharp metal edges.
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.