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 — Atto 3

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.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Aging or poor contact of the internal resistance wire in the left curtain airbag module (gas generator), resulting in increased internal resistance.
  • 2Roof wiring harness connector (usually located inside the A-pillar or B-pillar trim) is loose, oxidized, or corroded due to water ingress, causing increased contact resistance.
  • 3Repeated door operation wears and breaks the wiring harness at the roof crossmember, reducing the conductor cross-sectional area.
  • 4Reference voltage drift in the SRS control unit internal monitoring circuit, or a sampling resistor fault, causing a false code (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 and 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 and 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 model workshop manual for pin definitions). Normal value: 1.5-2.5 Ω. If the resistance is >3.0 Ω, continue troubleshooting.
  • 4
    Sectional 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. Ensure connector locking tabs are fully engaged.
  • 6
    System Verification: Restore all connections, refit 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-check' and 'crash sensor calibration' procedures. Confirm 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.