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B1726

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

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 — Qin Plus
  • 1Right knee airbag igniter internal short circuit: 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 bites damaged 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 vehicle 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 disengage, resulting in 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 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 (Active) fault, not a history fault. Clear the fault code. If the code returns immediately, confirm a continuous fault.
  • 3
    Visual inspection: Remove the front passenger lower dashboard trim panel. Check the right knee airbag wiring harness (yellow sleeve) for obvious damage or crushing. 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 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 instrument panel). Measure the continuity and insulation of the harness between the ECU terminals and the knee airbag connector terminals. Check for a short to ground or a short to power.
  • 6
    Shorting bar test: Check the knee airbag connector shorting bar function. The shorting bar must short the two terminals upon disconnection (to prevent accidental deployment from static electricity) and fully open upon connection. If a stuck shorting bar causes a continuous short, 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 with the front facing a safe direction). If the fault transfers, the airbag module is faulty.
  • 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-test. Confirm B1726 does not return and verify the airbag warning light turns off after the self-test.
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 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.