AU
B1706-00

This DTC indicates the Airbag Control Unit (ACU) detects an abnormal short circuit between the ignition drive circuit of the Left Side Curtain Airbag (located inside the driver-side roof side rail) and the vehicle constant power supply (B+) — Atto 8

Safety System

This DTC indicates the Airbag Control Unit (ACU) detects an abnormal short circuit between the ignition drive circuit of the Left Side Curtain Airbag (located inside the driver-side roof side rail) and the vehicle constant power supply (B+).

Under normal conditions, the ACU internal boost circuit supplies a high-voltage pulse to the airbag ignition circuit only at the moment of deployment, and the circuit remains insulated from body ground and power lines.

When the diagnostic system detects a continuous 12V battery voltage in this circuit, it identifies a short to power.

This fault causes the ACU to trigger primary/secondary safety protection and disable the left curtain airbag circuit to prevent accidental deployment, resulting in a loss of head protection during a side-impact collision.

If the short-circuit current reaches the deployment threshold, extreme cases may cause unexpected airbag deployment, constituting a severe safety defect.

The B1706-00 fault code on the Atto 8 indicates a high-severity short to battery power in the left side curtain airbag ignition circuit. This can disable the curtain airbag and may affect crash protection. Common causes include damaged roof or pillar wiring, or a loose headlining harness rubbing on sharp metal. The recommended fix is to visit an authorised dealer for inspection and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1The left curtain airbag wiring harness chafes against a body constant power wire (such as the reading light, sun visor light, or roof ambient light power wire) inside the A-pillar or C-pillar trim panel, causing insulation damage and a short to positive.
  • 2Detached headlining wiring harness retaining clip above the front seats causes the harness to sag and rub against the sharp metal edge of the roof crossmember, exposing the positive wire and causing it to contact the curtain airbag circuit.
  • 3Vehicle wading or a blocked sunroof drain hose causes water ingress and corrosion at the left curtain airbag connector (usually located inside the B-pillar or C-pillar), creating a conductive path between the pins.
  • 4During improper aftermarket modifications (such as routing dash cam wiring through the headliner or installing aftermarket audio tweeters), a screw pierces the wiring harness insulation and shorts the curtain airbag igniter wire to a constant power circuit.
  • 5Internal breakdown of the airbag control unit ignition driver chip or a shorted power transistor causes continuous high-level output to this circuit.
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the 12V battery negative terminal, and wait at least 3 minutes to fully discharge the ACU energy storage capacitor. Do not work on the airbag system with the ignition switch ON.
  • 2
    Fault confirmation: Use the BYD dedicated diagnostic tool (VDS2000 or VDS2100) to read the DTC. Confirm B1706-00 is a current fault, not a history fault. Check the voltage value in the freeze frame data (usually displays as abnormally high voltage B+).
  • 3
    Visual inspection: Remove the left A-pillar trim, left front headliner trim panel, and C-pillar trim. Check the wiring harness for obvious damage or burn marks. Focus on contact points with body metal edges or screws.
  • 4
    Circuit measurement: Disconnect the ACU connector. Use a multimeter to measure the voltage to ground at the left curtain airbag deployment terminals (usually specified pins, such as 26# and 27#). The normal reading is 0 V. If the reading is 12 V, trace the wiring toward the curtain airbag to locate the short circuit.
  • 5
    Section isolation: Disconnect the plug at the curtain airbag connector. Measure continuity to ground on the ACU-side harness and the curtain airbag-side harness separately to determine if the short circuit is in a harness section or the module itself.
  • 6
    Repair procedure: If the wiring harness is damaged, repair it with heat-shrink tubing or waterproof tape and re-secure it; if the connector has water ingress, dry it thoroughly, apply conductive grease, and replace the plug if necessary; if the ACU has an internal short circuit, replace the airbag control unit.
  • 7
    System verification: Reconnect all connectors, connect the negative battery terminal, and clear the fault code using the diagnostic tool. Perform the 'Airbag System Self-Learning' or 'Configuration Write' procedure. Verify B1706-00 does not return and the airbag warning lamp turns off.
Real-World Cases
BYD DTC AI Analysis

A-pillar trim screw pinching damaged the wiring harness.

✓
A 2017 Qin EV300 exhibited an airbag warning light that stayed on after accident repairs. Diagnosis confirmed active fault code B1706-00. Getting under the left A-pillar trim revealed that the trim panel screws replaced during the accident repair were too long, piercing the outer insulation of the left curtain airbag harness. This shorted the yellow igniter wire to the red constant-power wire for the reading lamp. Repair: Replaced the damaged harness section (the complete main harness from the ACU to the curtain airbag), sleeved it with genuine convoluted tubing for added protection, and installed standard-length screws. Fault cleared.
BYD DTC AI Analysis

Sunroof drain tube leak caused connector corrosion

✓
A 2018 Qin EV450 had an airbag warning light on after the rainy season. The owner reported water stains on the left headliner. Inspection revealed DTCs B1706-00 accompanied by B1707-00 (right curtain airbag short to ground). Removed the C-pillar trim and found severe corrosion on the left curtain airbag connector, with verdigris between the pins shorting positive to negative. Traced the leak to a detached left rear sunroof drain hose, allowing rainwater into the C-pillar. Repaired the drain hose connection, thoroughly dried the C-pillar interior, cleaned the connector with precision electronics cleaner, applied dedicated conductive grease, and replaced the curtain airbag wiring harness plug. Fault resolved.
BYD DTC AI Analysis

Aftermarket headliner ambient lighting caused circuit interference.

✓
A 2017 BYD Qin 100’s airbag warning light illuminated after an auto accessory shop installed aftermarket interior roof ambient lighting. The system stored DTC B1706-00. Inspection found the installer had bundled the ambient lighting power feed (constant power) together with the left curtain airbag harness using cable ties, and secured the light strip with metal self-tapping screws. The screws pierced the airbag harness insulation, causing a short circuit. Fix: removed the non-compliant ambient lighting and wiring, repaired the damaged curtain airbag harness by soldering and heat-shrink tubing, restored the original harness routing, and cleared the DTCs. The system returned to normal.
BYD DTC AI Analysis

Internal driver chip shorted in airbag control unit

✓
A 2017 Qin 80 with no accident or modification history suddenly had the airbag warning light come on while driving, displaying DTC B1706-00. Measured the left curtain airbag drive terminal at the ACU connector: constant 12V output. Disconnected the connector and measured continuity from the ACU internal to the curtain airbag terminal, confirming the internal ignition drive circuit had shorted. Replaced the airbag control unit (ACU). Ran the 'ECU Replacement' procedure using VDS, wrote the vehicle VIN and configuration, and executed a system self-test. Fault resolved.
BYD DTC AI Analysis

Seat adjustment mechanism rubbing against wiring harness

✓
A 2018 BYD Qin EV450 developed an intermittent DTC B1706-00, particularly after adjusting the driver's seat height. Inspection found the left curtain airbag wiring harness routed too close to the seat frame below the B-pillar. When the seat was raised to its highest position, the seat frame edge chafed against the harness, wearing through the insulation and exposing the copper wire, which shorted to the seat motor power line. We rerouted the harness, secured it clear of the seat track using dedicated harness retaining clips, fitted protective sleeving at the wear point, and replaced the damaged harness section.
Other Atto 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.