AU
B1727-00

This DTC indicates the Airbag Control Unit (ACU) detects the right knee airbag (front passenger knee airbag) squib circuit resistance is below the system calibration threshold (typically <1 — Atto 8

Safety System

This DTC indicates the Airbag Control Unit (ACU) detects the right knee airbag (front passenger knee airbag) squib circuit resistance is below the system calibration threshold (typically <1.0Ω; normal range: 2.0-3.0Ω).

Low resistance indicates an abnormally low-resistance path in the circuit.

A short to ground, a wire-to-wire short, or an internal short in the airbag squib typically causes this condition.

This fault presents two severe risks: first, short-circuit current can trigger unintended airbag deployment, injuring occupants; second, excessive circuit current during a collision can burn the contacts, preventing airbag deployment.

This fault constitutes an active safety system failure.

The vehicle remains drivable, but the airbag system enters degraded protection mode.

During a collision, the right knee airbag and any other airbags with related faults will fail to deploy.

The B1727-00 fault code on the Atto 8 indicates low resistance in the front passenger right knee airbag squib circuit, usually caused by a short circuit. Severity is medium because the airbag system may enter degraded mode, with a risk of unintended deployment or failure to deploy in a crash. Common causes include a damaged yellow airbag wiring harness or an internal short in the knee airbag inflator. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Internal short circuit in the knee airbag inflator: Manufacturing defects or moisture ingress damage the igniter bridge wire insulation inside the airbag assembly, causing an internal short circuit.
  • 2Physical damage to the wiring harness: During dashboard removal and installation, carpet replacement, or front passenger glove box repair, the metal frame crushes or cuts the knee airbag wiring harness (usually in a yellow sleeve), causing a short to ground.
  • 3Connector water ingress and corrosion: Water from vehicle wading, A/C condensate leaks, or floor cleaning enters the airbag connector under the front passenger floor (usually located under the lower center console or front passenger seat), causing an electrolytic short circuit between the terminals.
  • 4SRS control module internal drive circuit fault: ACU internal ignition drive transistor breakdown or sampling resistor circuit fault, causing a false low resistance reading.
  • 5Improper operation or modification: Unqualified personnel accidentally pierce the airbag wiring harness while installing a dash cam, ambient lighting, or audio system in the front passenger area, causing the copper core to short to ground.
What To Do
  • 1
    Safety preparation and diagnostic confirmation: Use the BYD ED400/ED600 diagnostic tool to read the DTC. Confirm B1727-00 is a current fault and the freeze frame data shows abnormal resistance (usually <0.5Ω). Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor.
  • 2
    Visual inspection and location: Remove the passenger-side lower dashboard trim panel (knee bolster). Inspect the yellow connector on the right knee airbag module (located on the frame beneath the glovebox) for looseness, water ingress, or obvious corrosion. Check the wiring harness for signs of frame edge crush damage or screw punctures.
  • 3
    Segmented resistance measurement: Use a dedicated airbag tester (low-current mode <10mA) or a digital multimeter (resistance mode only). Disconnect the airbag connector and measure the following separately: ① resistance between airbag-side terminals (normal: 2.0-3.0Ω); ② resistance from the harness side to ground (should be infinite); ③ resistance between harness-side terminals (should be infinite, ruling out a short circuit between harness wires).
  • 4
    Harness circuit inspection: If the airbag resistance is normal, bridge the harness-side connector using a jumper wire, then measure harness continuity and resistance at the SRS module connector. Inspect the protective rubber sleeves at the firewall and floor channel for damage. Specifically check the harness above the front passenger footwell for interference with the air conditioning duct metal bracket.
  • 5
    Insulation repair or replacement: If the wiring harness is damaged, repair it using heat-shrink tubing or insulating tape and re-secure the harness. Maintain a >20mm clearance from sharp metal edges. If the airbag module resistance is abnormal (<1.0Ω), replace the right knee airbag assembly (part number usually starts with 57). Never repair the airbag.
  • 6
    System reset and verification: Restore all connections, reconnect the battery, and clear the fault code. Perform the SRS system self-test (usually requires turning the ignition switch to the ON position and waiting 6 seconds) and confirm B1727-00 does not return. Perform a wiggle test: gently wiggle the knee airbag wiring harness by hand and verify the 'right knee airbag resistance' in the diagnostic tool data stream remains stable within the 2.0-3.0Ω range.
  • 7
    Final confirmation: Use the diagnostic tool to perform 'Crash Sensor Calibration' or 'SRS System Configuration' (if replacing the airbag or ACU). Confirm the instrument cluster SRS warning light turns off and the system status displays 'Normal'.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 right knee airbag short circuit after wading

✓
A 2018 BYD Qin EV450 displayed "Check SRS System" on the dashboard after driving through floodwater during heavy rain. The scan tool retrieved B1727-00 (current fault). Inspection found water pooling in the front passenger footwell. After removing the front passenger seat and lower centre console trim, the knee airbag connector (located inside the front passenger seat rail) showed visible water staining and the terminals had green corrosion. Cleaning and drying the connector still yielded low resistance readings; further inspection revealed water had penetrated the airbag igniter. Replaced the right knee airbag assembly and resealed the floor waterproofing to resolve the fault.
BYD DTC AI Analysis

Qin 80 wiring harness crushed after accident repair

✓
One month after a front collision repair, this 2017 Qin 80 set DTC B1727-00. During the repair, the technician replaced the dashboard and passenger airbag but did not properly secure the knee airbag harness. Inspection found a screw at the dashboard frame mounting point had crushed the harness, damaging the insulation and causing a short to ground. They rerouted the harness, fastened it with dedicated clips, and made sure it had enough clearance from the frame edges. After repairing the insulation, the fault cleared; the airbag unit itself was not replaced.
BYD DTC AI Analysis

Qin 100 air conditioning water leak caused connector corrosion

✓
The owner reported that the airbag warning light occasionally illuminated. The scan tool retrieved historical fault code B1727-00. Inspection revealed a blocked passenger-side air conditioning evaporator drain hose, causing condensate to overflow onto the floor. The knee airbag connector, located above the passenger footwell, had been exposed to prolonged moisture, resulting in a micro-short between terminals. Cleaned the connector terminals, applied conductive anti-corrosion compound, unclogged the drain hose, and wrapped the connector with waterproof tape. Measured resistance returned to normal. One-month follow-up showed no recurrence.
BYD DTC AI Analysis

SRS module false alarm causing abnormal resistance

✓
2017 Qin EV300 frequently setting DTC B1727-00, but measured resistance of knee airbag and harness was normal (2.3Ω). Harness: no short circuits; airbag: intact. Suspected internal sampling circuit fault in SRS control module (ACU). Swapped in a known-good ACU from another vehicle for testing; fault transferred with the module. After reinstalling original ACU, fault returned. Replaced airbag control module and reconfigured vehicle VIN and crash sensor parameters. Fault permanently resolved.
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.