AU
B170A

DTC B170A indicates the Left Side Curtain Airbag ignition circuit resistance exceeds the normal threshold set by the SRS control unit (typically >3 — Seal U

Safety System

DTC B170A indicates the Left Side Curtain Airbag ignition circuit resistance exceeds the normal threshold set by the SRS control unit (typically >3.0 Ω, standard range 1.5–2.5 Ω).

This Level 2 airbag system fault means the Left Side Curtain Airbag may fail to deploy normally or experience delayed deployment during a collision, severely compromising side-impact occupant protection.

High resistance typically indicates a high-impedance point in the circuit, such as a partially broken wire, increased connector contact resistance, oxidation, corrosion, or an internal open circuit in the airbag inflator.

The SRS control unit continuously monitors this circuit.

Upon detecting abnormal resistance, the unit illuminates the airbag fault warning lamp and may disable the entire airbag system to prevent accidental deployment.

The B170A fault code on the Seal U indicates medium-severity high resistance in the left side curtain airbag ignition circuit. This may prevent or delay airbag deployment in a side impact and can trigger the airbag warning light. Common causes include a loose, oxidized, or corroded roof harness connector, or increased internal resistance in the curtain airbag module. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Aging or poor contact of the internal resistance wire in the left-side curtain airbag module (gas generator) increases internal resistance.
  • 2Roof wiring harness connector (usually located inside the A-pillar or B-pillar trim) is loose, oxidized, or corroded from water ingress, increasing contact resistance.
  • 3Repeated door opening and closing wears and breaks the roof crossmember wiring harness, reducing the conductor cross-sectional area.
  • 4Reference voltage drift in the SRS control unit internal monitoring circuit or a sampling resistor fault causing false reporting (less common)
  • 5Driving through water or a blocked sunroof drain hose causes water ingress at the left curtain airbag wiring harness connector, resulting in terminal corrosion.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal. Wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Initial inspection: Remove the left A-pillar and B-pillar trim panels. Visually inspect the curtain airbag wiring harness connector (usually a yellow plug) for looseness, backed-out terminals, oxidation, or signs of water ingress.
  • 3
    Resistance measurement: Disconnect the SRS control unit connector and use a multimeter to measure the left curtain airbag circuit resistance (refer to the specific vehicle workshop manual for pin definitions). The normal value is 1.5-2.5 Ω. If the resistance is >3.0 Ω, continue troubleshooting.
  • 4
    Section isolation: Disconnect the roof wiring harness from the curtain airbag module and directly measure the resistance between the two terminals of the airbag module. If the resistance is normal, the fault is in the wiring harness. If the resistance remains high, replace the left curtain airbag module.
  • 5
    Wiring harness repair: Check the roof wiring harness for wear at the roof side rail and door hinges. Repair damaged wires. Clean oxidized terminals and apply conductive grease. Fully engage the connector locking tabs.
  • 6
    System verification: Reconnect all connectors, reinstall the trim panels, and connect the battery. Clear the fault code using a diagnostic tool such as VDS or Launch X-431. Perform the 'SRS system self-check' and 'crash sensor calibration' procedures. Verify B170A does not return and the warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Oxidation of the left A-pillar connector on a Song MAX caused high resistance.

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A 2019 BYD Song MAX came in with the airbag warning light constantly on. The technician retrieved fault code B170A. After removing the left A-pillar trim, the technician found obvious oxidation inside the yellow curtain airbag harness connector, with blackened terminals. The technician cleaned the terminals with electronic contact cleaner, applied conductive grease, and reconnected the harness. The resistance reading returned to 2.1 Ω. After clearing the fault code and road testing, the fault was resolved. The cause was long-term parking in a humid environment and a deteriorated A-pillar weatherstrip that allowed moisture ingress.
BYD DTC AI Analysis

Headliner wiring harness chafing caused intermittent B170A fault on Tang DM

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The owner of a 2021 Tang DM reported that the airbag warning light occasionally illuminates, more frequently when cold. A diagnostic scan retrieved historical fault code B170A; current resistance measured 2.8Ω (borderline high). Inspection found insulation wear on the left side curtain airbag wiring harness at the roof crossbeam retaining clip from prolonged vehicle vibration. The copper wires had partially fractured, with only a few strands remaining connected, causing unstable resistance. The technician replaced the headliner wiring harness assembly; a local repair would not meet safety requirements. The fault was completely resolved.
BYD DTC AI Analysis

Yuan EV: Curtain airbag connector left disconnected after sunroof replacement, causing fault

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A 2019 Yuan EV logged DTC B170A after sunroof repairs at an unauthorized workshop. Inspection found that during headliner removal and reinstallation, the technician had not fully plugged in the left side curtain airbag harness connector, causing poor contact between the male and female terminals. Resistance measured 4.2 ohms. Re-seating the connector and confirming the locking tab clicked into place reduced resistance to 1.9 ohms. This case serves as a reminder: after any headliner removal, always check all SRS connectors.
BYD DTC AI Analysis

BYD Qin Pro Left Side Curtain Airbag Module Internal Open Circuit Replacement Case

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2020 Qin Pro petrol. After accident repairs, replaced the deployed left curtain airbag with a new unit, but DTC B170A set after installation. Measured infinite resistance on the new part — quality defect (internal igniter open circuit). Installed a genuine OEM left curtain airbag module (part number matched to VIN). Measured resistance: 2.0Ω, normal. After coding the new airbag module, the fault cleared. Airbag components must be genuine OEM parts; do not interchange arbitrarily.
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U overview →
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.