AU
B1726

DTC B1726 indicates the SRS (Supplemental Restraint System) control unit detects a Right Knee Airbag circuit resistance of 0Ω or near 0Ω — Atto 3

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.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Internal short circuit in right knee airbag igniter: Moisture, aging, or manufacturing defects cause the igniter bridge wire inside the airbag module to short between the positive and negative terminals.
  • 2Harness short to ground: Wear, crushing, or rodent bites damage 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), shorting the harness to body ground.
  • 3Connector fault: Knee airbag connector (usually located behind the glovebox or on the dashboard 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 incorrectly reports the resistance value as 0 while the actual circuit is normal.
  • 5External interference or water ingress: Vehicle wading or an A/C condensate leak 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 discharge the SRS capacitor fully). Use a multimeter to confirm the system has no residual high voltage.
  • 2
    Fault confirmation: Connect the diagnostic tool, read the DTC, and record the freeze frame data. Confirm B1726 is a current (Active) fault, not a historical fault. Clear the fault code. If the code reappears immediately, the fault is persistent.
  • 3
    Visual inspection: Remove the passenger-side lower dashboard trim panel. Check the right knee airbag wiring harness (yellow sleeve) for obvious damage or crushing marks. Check the connector for looseness, water ingress, or corrosion.
  • 4
    Resistance measurement: Disconnect the knee airbag connector. 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 must 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 terminal and the knee airbag connector terminal. Check for short to ground or short to power.
  • 6
    Shorting bar test: Check the knee airbag connector shorting bar function. The bar must short the two terminals when disconnected to prevent accidental deployment from static electricity, and fully open the circuit when connected. If a sticking shorting bar 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 the test and point the front in a safe direction). If the fault transfers, this confirms the airbag module is faulty.
  • 8
    SRS ECU inspection: If the 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.