AU
B170A1B

This DTC indicates the Supplemental Restraint System (SRS) detected the igniter (squib) circuit resistance of the left curtain shield airbag (located above the driver-side window between the B-pillar and C-pillar) exceeds the calibrated threshold (typically >3 — Atto 8

Safety System

This DTC indicates the Supplemental Restraint System (SRS) detected the igniter (squib) circuit resistance of the left curtain shield airbag (located above the driver-side window between the B-pillar and C-pillar) exceeds the calibrated threshold (typically >3.6Ω, normal range 1.5-3.0Ω).

Excessive resistance usually indicates a high-resistance connection, a partial open circuit, poor connector contact, or an internal open circuit in the igniter.

This fault may prevent the left curtain shield airbag from deploying during a side impact and continuously illuminates the SRS warning light.

This is a critical fault affecting passive safety.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Loose connection, backed-out pins, or oxidized terminals at the left lower A-pillar curtain airbag wiring harness connector (yellow plug), causing increased contact resistance.
  • 2Internal open circuit or poor contact in the spiral cable (clock spring) affecting signal transmission in the curtain airbag circuit (on some models, the curtain airbag circuit routes near the steering column).
  • 3Internal open circuit or aging failure of the curtain airbag igniter causes infinite or abnormally high circuit resistance.
  • 4Airbag Control Module (ACM/SRS ECU) internal detection circuit fault, abnormal sampling resistor, or connector pin corrosion
  • 5Long-term bending and wear of the body wiring harness at the A-pillar or B-pillar pass-through breaks copper strands, creating a high-resistance connection.
What To Do
  • 1
    Safety preparation: Turn the vehicle OFF, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use the BYD VDS diagnostic tool to read freeze frame data, confirm the exact current resistance value of the left curtain airbag (e.g., 3.8Ω or OL open circuit), and check for intermittent faults.
  • 3
    Visual inspection: Remove the left A-pillar trim panel and front roof trim panel. Verify the curtain airbag wiring harness connector (yellow waterproof plug) is fully locked. Inspect for water ingress, oxidation, burn marks, or backed-out pins.
  • 4
    Wiring inspection: Disconnect the ACM connector and use a dedicated low-current ohmmeter (<10mA) to measure harness continuity from the ACM pin to the curtain airbag connector. Normal resistance is <1Ω. Check the harness insulation at the A-pillar pass-through hole for wear.
  • 5
    Component isolation test: Connect a 2 Ω SRS simulator resistor to the circuit in place of the curtain airbag assembly. If the fault code clears, the curtain airbag assembly is faulty; if it remains, check the wiring harness or ACM.
  • 6
    Repair/Replace: Repair the damaged wiring harness and re-wrap with anti-abrasion tape. Replace the faulty curtain airbag assembly (install new retaining clips and bolts simultaneously). Replace the ACM if necessary.
  • 7
    System verification: Reconnect the battery, clear the fault code, and perform an SRS system self-check (turn the ignition switch ON and verify the warning lamp illuminates then turns off). Use the VDS to read the current resistance and confirm it has returned to the normal range (1.5-3.0 Ω).
Real-World Cases
BYD DTC AI Analysis

Qin PRO DM A-pillar connector oxidised after water exposure, causing high resistance

✓
After driving through water, the SRS warning light stayed on. Retrieved DTC B170A1B; freeze frame data showed 4.2 Ω resistance. Removed the left A-pillar trim and found obvious water stains and white oxidation powder inside the curtain airbag harness connector (yellow). Cleaned the connector terminals and applied conductive protectant — resistance returned to 2.1 Ω and the fault cleared. Check the door seals and A-pillar drain holes for blockages.
BYD DTC AI Analysis

Left curtain airbag connector not fully seated after interior trim removal and refitting

✓
After removing the left A-pillar trim for audio system modification, the SRS warning lamp illuminated. Diagnosis showed current DTC B170A1B. Inspection found the curtain airbag connector was inserted, but the CPA (Connector Position Assurance) was not fully engaged, causing poor terminal contact. Reconnected the connector firmly until an audible click confirmed the lock, then used VDS to clear the fault codes. System returned to normal.
BYD DTC AI Analysis

Internal open circuit in clock spring causes intermittent warning

✓
The SRS warning light occasionally illuminated while driving, clearing after restarting. Diagnostics revealed intermittent DTC B170A1B with resistance fluctuating between 2.8 Ω and open circuit. Traced the left curtain airbag circuit through the clock spring (spiral cable) beneath the combination switch and identified an internal break in the flat ribbon cable. Replaced the clock spring and verified the repair by repeatedly turning the steering wheel; the fault did not return.
BYD DTC AI Analysis

Curtain airbag igniter body internal open circuit

✓
Vehicle repaired after collision. Replaced left curtain airbag but DTC B170A1B remained. Old airbag resistance: OL (open circuit); new airbag: 2.2 Ω (normal). Fault persisted after fitting. Further inspection found the crash crushed and deformed the wiring harness inside the B-pillar, partially fracturing internal copper wires and creating high resistance. Replacing the wiring harness resolved the fault.
Other Atto 8 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.