AU
B1723

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

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.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1A worn or crushed right knee airbag wiring harness causes a short circuit to the power wiring harness. Tight wiring routing under the dashboard or metal edge burrs cutting the insulation typically cause this.
  • 2Airbag connector (usually located behind the glove box or on the right side of the dashboard): Water ingress, oxidation, or deformed terminals causing a short circuit between the power and signal terminals.
  • 3Internal short circuit between layers in the clock spring (spiral cable). The knee airbag circuit usually bypasses the steering wheel clock spring, but the fault may involve an intermediate connector on some models.
  • 4SRS ECU internal drive circuit fault causing a false short to power, 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 a dedicated BYD diagnostic tool (VDS or ED400) to read the fault codes, confirm B1723 is a Current fault rather than a History fault, and check for other SRS fault codes.
  • 2
    Disconnect the negative battery 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 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 and 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 harness. If the resistance is infinite, the airbag assembly may be faulty.
  • 5
    Follow the right knee airbag wiring harness routing (typically along the dashboard crossmember). Inspect the harness sleeve for wear, scorching, or metal clip pinch marks. Focus on contact points with the dashboard 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: 2.0-5.0 Ω), 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. Fully engage all yellow SRS connector locking tabs.
  • 9
    Reconnect the battery, clear the fault code, and turn the ignition switch to ON. Verify the SRS warning light 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 return.
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 Qin Plus 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.