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 U

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 U indicates the SRS control unit has detected a short circuit in the right knee airbag circuit, with resistance near 0Ω instead of the normal 1.5–3.0Ω. This is a medium-severity fault that may stop the airbag deploying and can disable the SRS. 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 U
  • 1Right knee airbag igniter internal short circuit: Moisture, aging, or manufacturing defects cause the igniter bridge wire inside the airbag module to short circuit between the positive and negative terminals.
  • 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 side of the center console), causing a short to body ground.
  • 3Connector fault: Knee airbag connector (usually located behind the glovebox or instrument panel crossmember) improperly locked, bent terminals causing a short circuit, or shorting bar failing to open normally, causing a continuous short circuit.
  • 4SRS control unit internal fault: Damaged ECU internal monitoring circuit falsely reports the resistance value as 0, while the actual circuit is normal.
  • 5External interference or water ingress: Vehicle wading or air conditioning condensate leakage causes water ingress and a short circuit at the wiring harness connector in the knee airbag area (above the front passenger floor).
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (to fully discharge the SRS capacitor). Use a multimeter to confirm no residual high voltage remains in the system.
  • 2
    Fault confirmation: Connect the diagnostic tool, read the DTC, and record the freeze frame data. Confirm B1726 is a current fault (Active), not a historical fault. Attempt to clear the fault code. If it reappears immediately, confirm the fault is persistent.
  • 3
    Visual inspection: Remove the front passenger side lower dashboard 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 resistance should be infinite. If continuity exists, repair the wiring harness.
  • 5
    Harness continuity check: Disconnect the SRS ECU connector (located in the center tunnel or behind the dashboard). 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 open completely when connected. If the shorting bar sticks and causes a continuous short, repair or replace the connector.
  • 7
    Replacement test: If the wiring harness is normal but the fault persists, perform a replacement test with a known-good knee airbag (Note: Secure the airbag during testing and point the front in a safe direction). If the fault transfers, this confirms the airbag module is damaged.
  • 8
    SRS ECU inspection: If all above checks are normal, measure the internal resistance of the corresponding SRS ECU terminal. If internally shorted, 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 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.