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+) — Seal 6 EV

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 Seal 6 EV indicates a high-severity short to battery power in the left side curtain airbag ignition circuit. This can disable the curtain airbag and may create a risk of unintended deployment. Common causes include damaged wiring near the A- or C-pillar, or a loose headliner harness rubbing on metal edges. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1The left curtain airbag wiring harness chafes against a vehicle constant power wire (such as the reading lamp, sun visor lamp, or headlining ambient light power wire) inside the A-pillar or C-pillar trim panel, causing insulation damage and a short to positive.
  • 2The headliner wiring harness retaining clip above the front seats detached, causing the harness to sag and rub against the sharp metal edge of the roof crossmember, exposing the positive wire and causing contact with the curtain airbag circuit.
  • 3Vehicle wading or a blocked sunroof drain hose causes water ingress and corrosion in the left curtain airbag connector (usually located inside the B-pillar or C-pillar), creating a conductive path between the pins.
  • 4During non-professional modifications (such as routing a dash cam cable through the headliner or installing aftermarket audio tweeters), a screw pierces the wiring harness insulation, shorting the curtain airbag ignition wire to a constant power circuit.
  • 5Internal breakdown of the airbag control unit ignition driver chip or a shorted power transistor, causing a 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 an abnormally high B+ voltage).
  • 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 curtain airbag connector. Measure continuity to ground on the ACU side and the curtain airbag side of the harness separately to determine whether the short circuit is in a specific harness section or the module itself.
  • 6
    Repair procedure: If the wiring harness is damaged, repair it using heat-shrink tubing or waterproof tape and re-secure it; if water has entered the connector, dry it thoroughly, apply conductive grease, and replace the plug if necessary; if testing confirms an internal short circuit in the ACU, replace the airbag control unit.
  • 7
    System verification: Reconnect all connectors, connect the battery negative terminal, use the diagnostic tool to clear the fault code, and perform the 'Airbag System Self-Learning' or 'Configuration Write' procedure. Confirm B1706-00 no longer appears and the airbag warning lamp turns off normally.
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 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.