AU
B1726

DTC B1726 indicates the SRS (Supplemental Restraint System) control unit detects a Right Knee Airbag circuit resistance of 0Ω or near 0Ω — Seal 6 EV

Safety System

DTC B1726 indicates the SRS (Supplemental Restraint System) control unit detects a Right Knee Airbag circuit resistance of 0Ω or near 0Ω.

Normal airbag inflator resistance is 1.5-3.0Ω.

A resistance of 0Ω indicates a short circuit in the airbag circuit.

Potential causes include an internal short in the airbag inflator, a wiring harness short to ground, or a short between connector terminals.

This fault causes the SRS to enter protection mode.

During a collision, the Right Knee Airbag may fail to deploy normally.

The system also illuminates the airbag warning light and may disable the entire airbag system to protect occupants.

The B1726 fault code on the Seal 6 EV indicates a short circuit in the Right Knee Airbag circuit, with resistance at or near 0Ω instead of the normal 1.5–3.0Ω. Severity is medium, as the airbag warning light may come on and the SRS may enter protection mode, possibly preventing normal airbag deployment. Common causes include a shorted airbag igniter or damaged wiring. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Internal short circuit in the right knee airbag igniter: Moisture, aging, or manufacturing defects cause a short circuit between the positive and negative terminals of the igniter bridge wire inside the airbag module.
  • 2Harness short to ground: Wear, crushing, or rodent damage breaks the insulation on the yellow dedicated harness from the SRS ECU to the right knee airbag (usually located under the dashboard, right of the center console), causing a short to the vehicle body ground.
  • 3Connector fault: Knee airbag connector (usually located behind the glovebox or at the instrument panel crossmember) improperly locked, bent terminals causing a short circuit, or shorting bar failing to disengage, causing a continuous short circuit.
  • 4SRS control unit internal fault: Damaged ECU internal monitoring circuit falsely reports a resistance value of 0, while the actual circuit is normal.
  • 5External interference or water ingress: Vehicle wading or A/C condensate leakage causes water ingress and a short circuit at the wiring harness connector in the knee airbag area (above the front passenger-side floor).
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (to ensure the SRS capacitor discharges completely). Use a multimeter to confirm the system has no residual high voltage.
  • 2
    Fault confirmation: Connect the diagnostic tool to read the DTC. Record freeze frame data and confirm B1726 is a current (Active) fault, not a history fault. Attempt to clear the fault code. If it reappears immediately, confirm a continuous fault.
  • 3
    Visual inspection: Remove the passenger-side dashboard lower trim panel. Check the right knee airbag wiring harness (yellow sleeve) for obvious damage or crush marks. Check the connector for looseness, water ingress, or corrosion.
  • 4
    Resistance measurement: Disconnect the knee airbag connector and use a digital multimeter to measure the resistance on the airbag side (normal: 1.5-3.0 Ω). If the resistance is 0 Ω, replace the airbag module. Measure the resistance to ground on the wiring harness side (ECU to connector). The reading must be infinite. If there is continuity, repair the wiring harness.
  • 5
    Harness continuity check: Disconnect the SRS ECU connector (located in the center tunnel or behind the instrument panel). Measure harness continuity and insulation between the ECU terminals and the knee airbag connector terminals. Check for a short to ground or power.
  • 6
    Shorting bar test: Check the knee airbag connector shorting bar function. The shorting bar must short the two terminals when disconnected (to prevent accidental deployment from static electricity) and fully open the circuit when connected. If the shorting bar sticks and causes a continuous short circuit, repair or replace the connector.
  • 7
    Substitution test: If the wiring harness is normal but the fault persists, perform a substitution test using a known-good knee airbag (Note: Secure the airbag during testing and face the front in a safe direction). If the fault transfers, the airbag module is damaged.
  • 8
    SRS ECU inspection: If the above checks are normal, measure the internal resistance of the corresponding SRS ECU terminal. If an internal short circuit exists, replace or repair the SRS control unit.
  • 9
    System reset and verification: After repair, reconnect all connectors and connect the battery. Use the diagnostic tool to clear the fault code and perform an SRS system self-check. Confirm B1726 does not return and verify the airbag warning light turns off after the self-check.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM right knee airbag wiring harness chafed and shorted

✓
A 2021 Tang DM with 32,000 km displayed 'Airbag System Fault' on the instrument cluster. Retrieved DTC B1726. Inspection found the passenger-side knee airbag wiring harness had chafed against the instrument panel crossbeam mounting bracket over time, wearing through the insulation and causing a short between the positive and negative wires. Repaired the damaged wiring with heat shrink tubing, rerouted the harness to clear the metal bracket, and fitted protective corrugated tubing. Fault resolved.
BYD DTC AI Analysis

BYD Song MAX knee airbag connector shorted due to water ingress

✓
2019 Song MAX developed DTC B1726 after driving through floodwater in heavy rain. Inspection found water pooling beneath the passenger side carpet; the knee airbag connector (mounted above the floor) showed internal corrosion causing a short between terminals. Cause: A blocked windscreen drainage channel allowed rainwater to leak into the cabin. Repair: Cleared the drainage channel, dried the wiring harness, cleaned the connector with electronic cleaner, applied conductive paste and reassembled. Fault cleared.
BYD DTC AI Analysis

Internal short circuit in BYD Yuan EV airbag module

✓
A 2019 Yuan EV suddenly showed the airbag warning light during normal use. The scan tool indicated the right knee airbag resistance was 0 Ω. After disconnecting the airbag connector, the module-side resistance measured 0.2 Ω (normal >1.5 Ω), confirming an internal short in the airbag igniter. Replaced the right knee airbag module (requires removing the lower instrument panel trim), reconfigured the SRS system (some models require special equipment to write the configuration code), resolving the fault.
BYD DTC AI Analysis

BYD Qin petrol SRS ECU false positive fault

✓
2020 BYD Qin petrol variant logged DTC B1726 following accident repairs. Replaced the right knee airbag but the fault remained. Tested wiring harness continuity: normal, resistance 2.1 Ω. Further inspection revealed the SRS ECU had suffered impact damage during the collision, damaging its internal monitoring circuit and causing a false zero-resistance reading. Replaced the SRS control unit (located beneath the centre console armrest). After VIN matching and system calibration, the fault was eliminated.
BYD DTC AI Analysis

Aftermarket floor mats crushed the wiring harness, causing a short circuit.

✓
The owner fitted full-coverage floor mats and a B1726 fault appeared one week later. Inspection found the passenger-side floor mat clip screws were too long. They had pierced the floor wiring harness protective layer and punctured the yellow knee airbag wire, causing a short circuit. We replaced the damaged harness section (from the main harness to the airbag), repositioned the floor mat clips, and fitted OEM short-type fixing screws. Fault resolved.
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.