AU
B1723

This DTC indicates a short to vehicle power (B+) in the SRS (Supplemental Restraint System) Right Knee Airbag ignition circuit — Seal U

Safety System

This DTC indicates a short to vehicle power (B+) in the SRS (Supplemental Restraint System) Right Knee Airbag ignition circuit.

Under normal operating conditions, the airbag ignition circuit remains isolated from the power supply.

The SRS ECU triggers the circuit with a specific current only during a collision.

When the control unit detects a short to power in this circuit, it logs a severe fault, immediately illuminates the airbag warning lamp, and enters fail-safe mode.

This mode may disable the entire airbag system to prevent accidental deployment or system failure.

During a frontal collision, the knee airbag limits the forward movement of the occupant's lower limbs, preventing femur and hip injuries caused by the knees striking the instrument panel.

Therefore, this fault directly compromises occupant passive safety protection.

The B1723 fault code on the Seal U indicates a high-severity short to vehicle power in the SRS right knee airbag ignition circuit. This can switch on the airbag warning light and may disable the airbag system, reducing crash protection. Common causes include damaged or pinched wiring under the dashboard, water ingress, corrosion, or deformed airbag connector terminals. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Right knee airbag wiring harness wear or pinching causes a short circuit to the power harness. Tight harness routing under the dashboard or metal edge burrs cutting the insulation typically cause this.
  • 2Water ingress, oxidation, or deformed terminals at the airbag connector (usually located behind the glove box or on the right side of the dashboard), causing a short circuit between the power terminal and the signal terminal.
  • 3Internal short circuit between layers in the clock spring (spiral cable). The knee airbag typically does not route through the steering wheel clock spring, but some models use an intermediate connector.
  • 4SRS ECU internal drive circuit fault causing a false short-to-power report, or short circuit between ECU connector pins.
  • 5Insulation failure of the inflator igniter inside the knee airbag assembly causes the resistance wire to short to the housing (ground or power).
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS or ED400) to read fault codes. Confirm B1723 is a Current fault, not a History fault, and check for accompanying SRS fault codes.
  • 2
    Disconnect the battery negative cable and wait at least 90 seconds (120 seconds for some models) to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 3
    Remove the glove box or front passenger side lower trim panel. Locate the right knee airbag connector (usually a yellow waterproof plug) and inspect the connector for damage, water ingress, or signs of corrosion.
  • 4
    Disconnect the airbag connector. Use a multimeter to measure the resistance between the harness-side connector terminal and the vehicle power supply (B+). If the resistance is less than 1 Ω, this indicates a short to power in the wiring harness. If the resistance is infinite, the airbag assembly may be faulty.
  • 5
    Carefully inspect the right knee airbag wiring harness sleeve along its routing (usually along the instrument panel crossmember) for wear, scorching, or metal clip pinch marks. Focus on contact points with the instrument panel metal bracket and air conditioning duct edges.
  • 6
    If the wiring harness is normal, measure the resistance between the two terminals of the airbag assembly-side connector (normal value: 2.0-5.0Ω), and measure the resistance between each terminal and the airbag metal housing (normal value: infinite). If the resistance is abnormal, replace the knee airbag assembly.
  • 7
    Check the SRS ECU connector (usually located under the center console or center tunnel) for looseness or water ingress. Measure the continuity and insulation of the wiring harness between the ECU and the airbag.
  • 8
    Repair the shorted wiring harness (re-wrap or replace the harness section) or replace the faulty airbag assembly/connector. Ensure all yellow SRS connector locking tabs fully lock.
  • 9
    Reconnect the battery, clear the fault code, and turn the ignition switch to the ON position. Verify the SRS warning lamp turns off after a 6-second self-check. Use the diagnostic tool to perform the 'SRS System Self-check' or 'Crash Sensor Check' function and confirm B1723 does not reappear.
Real-World Cases
BYD DTC AI Analysis

2020 BYD Qin petrol — Right knee airbag wiring harness chafed and shorted

✓
A BYD Qin petrol with 32,000 km had its instrument panel SRS warning light staying on constantly. VDS diagnostics retrieved code B1723-00 (right knee airbag short to power). Removal and inspection revealed the right knee airbag wiring harness, where it runs through the dashboard crossmember, had chafed against a metal bracket edge over time, wearing through the insulation. The exposed copper wire contacted the bracket (grounded to the vehicle body and thus indirectly connected to the positive power circuit), creating a short circuit. Repair: Wrapped the damaged section with electrical tape, added a rubber grommet between the harness and bracket, and secured the setup with cable ties to eliminate the interference point. After clearing the fault code, the SRS system returned to normal.
Original source ↗
BYD DTC AI Analysis

2019 BYD Song MAX: Airbag connector short circuit after water ingress

✓
After driving through water in heavy rain, the dashboard displayed an airbag warning. A scan tool showed current fault code B1723. Inspection found water pooling on the passenger floor. The right knee airbag connector, located low behind the glovebox, had internal water ingress causing electrolytic shorting between terminals. Removed the connector, cleaned the terminals with anhydrous alcohol, dried them with compressed air, and applied electrical contact protectant. Checked the airbag assembly resistance: 3.2Ω (normal). Reconnected the connector, which resolved the fault. Recommended checking the vehicle seals and drain holes.
BYD DTC AI Analysis

2021 BYD Tang: False SRS ECU fault

✓
During PDI, the SRS warning light was on. No collision history. Scan showed DTC B1723-00. Inspected the right knee airbag harness: insulation good, connectors normal, airbag resistance 3.8 Ω (normal). Root cause: software bug in the SRS ECU falsely reports a short to power under voltage fluctuations during startup. Upgraded the SRS ECU firmware to V2.3 or higher; fault eliminated. Known TSB—check software version first.
BYD DTC AI Analysis

2019 BYD Yuan EV knee airbag assembly internal short circuit

✓
Following a collision repair where the front bumper and right knee airbag were replaced, DTC B1723 set and would not clear. The wiring harness showed no short circuits. Measuring the new airbag assembly revealed continuity between both terminals and the metal housing (0.5 Ω), pointing to a quality defect—damaged insulation on the internal gas generator. Replaced the knee airbag with a genuine assembly (Part No.: KPB-5820400). Resistance then measured 3.1 Ω with insulation to ground, and the fault cleared. For collision repairs, use genuine parts and check airbag resistance.
BYD DTC AI Analysis

Aftermarket installation damaged the wiring harness on the BYD Qin Pro.

✓
When installing a dashcam power cable under the passenger-side dashboard, the owner used a self-tapping screw to secure the wiring. The screw penetrated the dashboard and pierced the right knee airbag harness, creating a short between the power cable and airbag wiring. One week later, the SRS warning light came on and the system stored DTC B1723. During the repair, we removed the unauthorised wiring, repaired the damaged SRS harness (cut out the damaged section, re-crimped the terminals, and sealed with heat-shrink tubing), then restored the factory wiring layout. SRS wiring normally has yellow sleeving; avoid it when modifying.
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.