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 U

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 U indicates a high-severity short to battery power in the left side curtain airbag ignition circuit. This can disable the curtain airbag and, in rare cases, risk unintended deployment. Common causes include damaged wiring in the A- or C-pillar, or a loose headlining harness rubbing on metal. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1The left curtain airbag wiring harness chafes against a body constant power wire (such as for the reading light, sun visor light, or headlining ambient light) inside the A-pillar or C-pillar trim panel, causing insulation damage and a short to positive.
  • 2The headlining 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 at the left curtain airbag connector (usually located inside the B-pillar or C-pillar), creating a conductive path between the pins.
  • 4A screw pierces the wiring harness insulation during non-professional modifications (such as routing a dash cam cable through the headliner or installing aftermarket audio tweeters), shorting the curtain airbag igniter wire to a permanent live circuit.
  • 5Airbag control unit internal ignition driver chip breakdown or power transistor short circuit 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 dedicated BYD diagnostic tool (VDS2000 or VDS2100) to read the DTC. Confirm B1706-00 is a current fault, not a historical fault. Check the voltage value in the freeze frame data (usually showing an abnormally high B+ voltage).
  • 3
    Visual inspection: Remove the left A-pillar trim, left front headliner trim panel, and C-pillar trim. Inspect 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 and use a multimeter to measure the voltage to ground at the left curtain airbag deployment terminals (usually specified pins, such as 26# and 27#). Normal voltage is 0V. If 12V is present, trace the wiring toward the curtain airbag to locate the short circuit.
  • 5
    Segment isolation: Disconnect the curtain airbag connector plug. Separately measure continuity to ground on the ACU-side and curtain airbag-side harnesses to determine whether the short circuit is in a harness segment 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 the connector has water ingress, dry it thoroughly, apply conductive grease, and replace the plug if necessary. If testing confirms an internal ACU short circuit, replace the airbag control unit.
  • 7
    System verification: Reconnect all connectors, connect the negative battery terminal, and use the diagnostic tool to clear the fault code. Execute the 'Airbag System Self-learning' or 'Configuration Write' procedure. Verify B1706-00 does not return 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 U Fault Codes
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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.