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 6 EV

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 6 EV indicates medium-severity high resistance in the left side curtain airbag ignition circuit. This may prevent or delay airbag deployment in a side impact. Common causes include a loose, oxidized, or water-damaged roof harness connector, or increased internal resistance in the curtain airbag module. Visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Aging or poor contact of the internal resistance wire in the left curtain airbag module (gas generator) causes increased internal resistance.
  • 2Roof wiring harness connector (usually located inside the A-pillar or B-pillar trim) loose, oxidized, or corroded by water ingress, causing increased contact resistance.
  • 3The roof crossmember wiring harness wears and breaks from long-term door operation, reducing the conductor cross-sectional area.
  • 4Reference voltage drift in the SRS control unit internal monitoring circuit, or sampling resistor failure, causing a false fault (less common).
  • 5Vehicle wading or a blocked sunroof drain hose causes water ingress into the left curtain airbag wiring harness connector, resulting in terminal corrosion.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds for the SRS capacitor to discharge fully, preventing 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 water ingress.
  • 3
    Resistance measurement: Disconnect the SRS control unit connector. 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 measure the resistance directly across the two airbag module terminals. If the resistance is normal, the wiring harness is faulty. 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 hinge. Repair damaged wires, clean oxidized terminals and apply conductive paste, and fully engage the connector locking tabs.
  • 6
    System verification: Reconnect all connectors, reinstall the trim panels, and connect the battery. Use a diagnostic tool such as VDS or Launch X-431 to clear the fault code. Perform the 'SRS system self-test' and 'crash sensor calibration' procedures. Confirm B170A does not return and the warning light is 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 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.