AU
B1706

DTC B1706 indicates the SRS (Supplemental Restraint System) detected abnormal continuity between the left curtain airbag (CAB) driver circuit and the vehicle battery positive (B+) — Atto 8

Safety System

DTC B1706 indicates the SRS (Supplemental Restraint System) detected abnormal continuity between the left curtain airbag (CAB) driver circuit and the vehicle battery positive (B+).

This "short to power" means at least one of the two wires in the CAB deployment circuit (typically the high-side and low-side driver wires) is shorted to the 12V power supply, or the squib inside the CAB module has an internal short circuit.

The SRS ECU continuously monitors the CAB circuit resistance (normally 2-3 Ω) via its internal diagnostic circuit.

If the ECU detects an abnormally high voltage (approaching battery voltage) or abnormal resistance, it immediately sets this DTC and illuminates the airbag warning lamp.

Because a short circuit can cause unintended CAB deployment or prevent deployment during a collision, the system enters fail-safe mode and disables the left CAB.

This severely compromises occupant head protection during a side impact.

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Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Worn left curtain airbag wiring harness or damaged insulation contacting the A-pillar, roof side rail, or power wires in the wiring channel (such as reading light or sunroof motor power wires), causing a short circuit.
  • 2Moisture ingress or aging failure of the internal squib in the left curtain airbag module (inflator) causes an internal short circuit, usually presenting as abnormal resistance (<1Ω or >10Ω) at the curtain airbag connector.
  • 3Internal driver circuit fault in the SRS control unit (ACM) falsely reporting a short circuit; or bent or backed-out curtain airbag connector pins contacting an adjacent power supply pin.
  • 4Vehicle wading or a blocked sunroof drain hose causes water ingress and corrosion at the left curtain airbag connector (located at the upper A-pillar or near the roof lining), resulting in a short circuit between terminals.
  • 5Accidental piercing of the curtain airbag wiring harness during unprofessional modifications (such as routing dash cam cables or installing ambient lighting), or a detached wiring harness retaining clip causing long-term chafing against sharp metal edges.
What To Do
  • 1
    Safety precautions: Disconnect the 12V battery negative terminal and wait at least 90 seconds (some models require 3 minutes) to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 2
    Fault confirmation and freeze frame analysis: Use VDS or a dedicated diagnostic tool to read the fault code. Confirm whether B1706 is a current (Active) or history code. Record the vehicle status when the fault occurred (temperature, voltage, vehicle speed, etc.).
  • 3
    Wiring harness visual inspection: Remove the left A-pillar trim panel and left roof lining. Check the curtain airbag wiring harness (usually wrapped in yellow sleeving) for wear, crushing, water stains, or burn marks. Focus on the contact points between the wiring harness and the body sheet metal.
  • 4
    Electrical measurement diagnosis: Disconnect the SRS ECU and curtain airbag module connectors. Use a multimeter to measure both terminals of the curtain airbag wiring harness for voltage to ground and resistance to power: ① Measure the voltage between both curtain airbag connector terminals and body ground. Normal value: <1V. ② Check both terminals for a short to power. Normal condition: Open circuit (infinite resistance). ③ Measure the curtain airbag module resistance. Normal value: 2.0-3.0Ω.
  • 5
    Segmented isolation test: If the wiring harness has a short circuit, use the split-half method to narrow down the fault range (disconnect intermediate connectors) to determine whether the fault is in the harness segment or the module. If the harness is damaged, replace the entire harness segment (taping or wrapping is prohibited).
  • 6
    Component replacement and verification: After replacing the faulty curtain airbag module or repairing the wiring harness, reconnect all connectors and restore battery power. Use the diagnostic tool to clear the fault code and perform the 'SRS system self-check' or 'crash output check'. Confirm B1706 does not return and the system status displays 'normal'.
  • 7
    Final check: Refit all interior trim parts, perform a road test or simulation test, and confirm the airbag warning light turns off after self-check and no other related fault codes appear.
Real-World Cases
BYD DTC AI Analysis

BYD Song MAX: Chafed left A-pillar wiring harness caused DTC B1706

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A 2019 Song MAX with 80,000 km displayed 'Please check SRS system' on the instrument panel. Retrieved DTC B1706 (left curtain airbag short to power). Removing the left A-pillar trim revealed the retaining clip for the curtain airbag harness had come off at the upper corner, allowing the harness to chafe against the sheet metal edge. The insulation wore through, exposing the copper wires, which contacted the reading lamp power wire (12V). A continuity test confirmed a short to battery positive. Replaced the left curtain airbag harness assembly (including connector), re-secured the harness routing, and eliminated the fault.
BYD DTC AI Analysis

Sunroof leak caused curtain airbag connector corrosion on a BYD Tang DM

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2021 Tang DM, southern region owner. Airbag warning light illuminated after the rainy season. Scanner shows active B1706 fault. Inspected the left side curtain airbag connector (located at the front of the left headliner) and found obvious water staining and verdigris inside the connector, with abnormal resistance between terminals (0.5 Ω, near short circuit). Traced the cause to a detached sunroof drain hose connector that allowed rainwater ingress. Cleaned and dried the connector, replaced the left side curtain airbag module (internally moisture-damaged), and repaired the drain hose. Fault resolved.
BYD DTC AI Analysis

Modification damaged the curtain airbag wiring harness on a BYD Yuan EV.

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2019 BYD Yuan EV. While routing wiring for a self-installed dash cam, the owner used a metal pry bar to remove the A-pillar trim and accidentally pierced the left curtain airbag harness. The vehicle logged B1706 immediately upon startup the following day. Inspection found two pierced wires in the harness, one shorting to the reading light power supply. Because the damage was in the middle of the harness, the entire left curtain airbag harness (from SRS ECU to curtain module) was replaced and the owner received safety guidance on vehicle modifications.
BYD DTC AI Analysis

BYD Qin Pro SRS control unit false positive fault

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2020 Qin petrol. Intermittent B1706 DTC, sometimes self-clearing. Measured left curtain airbag harness resistance normal at 2.3Ω, with good insulation to power supply. Inspected SRS ECU connector and found no abnormalities. Suspected internal diagnostic circuit fault within SRS ECU. Performed substitution test using borrowed SRS ECU from identical model; fault did not reappear. Replaced SRS control unit (recoding and vehicle configuration required). Fault fully resolved.
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.