AU
B1726-00

DTC B1726-00 indicates the Airbag Control Module (ACM) detects an abnormal resistance of 0 ohms (or below 0 — Qin Plus

Safety System

DTC B1726-00 indicates the Airbag Control Module (ACM) detects an abnormal resistance of 0 ohms (or below 0.8 Ω) in the Passenger Knee Airbag igniter circuit, evaluating it as a wiring short to ground or an internal short circuit within the airbag module.

In BYD Qin series and similar models, this DTC strictly corresponds to the right knee airbag circuit.

However, the SRS systems in other models (such as Song Pro, Tang DM-i, and Qin Plus) define this code as a front passenger seat Occupant Classification Sensor (OCS) circuit fault.

Regardless of the specific definition, the SRS system detects abnormal circuit impedance in the passenger-side lower safety protection device.

This causes the system to enter fault protection mode, disable the airbag deployment function, and illuminate the instrument cluster airbag warning light.

A 0-ohm resistance typically indicates a short circuit risk; prevent accidental deployment or complete failure.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Right knee airbag module internal igniter short circuit: Moisture ingress, aging, or manufacturing defects in the airbag assembly cause a short circuit in the internal igniter wire.
  • 2Harness short to ground: The harness from the ACM to the right knee airbag has chafed or damaged insulation inside the instrument panel, behind the glovebox, or in the floor wiring channel, grounding to body metal.
  • 3Connector fault: Bent pins, oxidation, water ingress, or a loose connection at the airbag wiring harness plug (usually located under the passenger-side dashboard) cause a short circuit between the positive and negative terminals.
  • 4Airbag Control Module (ACM) internal fault: Damaged ACM detection circuit falsely reports a low-resistance fault.
  • 5Accident or modification damage: Improper front-end collision repairs pinching the wiring harness; or drilling during dash cam or ambient lighting installation damaging the SRS wiring harness.
What To Do
  • 1
    Safety Preparation and Initial Inspection: Disconnect the battery negative terminal and wait 3 minutes to discharge the SRS capacitor. Use VDS2000 or Launch X431 to read all fault codes. Confirm B1726-00 is a current fault. Check for accompanying communication fault codes (such as U0151).
  • 2
    Connector and visual inspection: Remove the passenger-side dashboard lower trim panel. Check the white/yellow 2-pin right knee airbag connector (located below the glove box or on the lower right side of the dashboard) for looseness, water ingress, or oxidation. Measure the resistance between the wiring harness terminals at the plug (normally open circuit, should not be 0).
  • 3
    Airbag module isolation test: Disconnect the right knee airbag connector. Measure the resistance between the airbag terminals using a dedicated SRS multimeter. Normal resistance is 2.0-3.0Ω. If the resistance is 0Ω, replace the airbag assembly. Measure the resistance between the wiring harness side and body ground. The resistance must be infinite; otherwise, locate the short circuit.
  • 4
    Detailed wiring harness routing inspection: Follow the airbag harness routing (from the ACM to the airbag, passing through the instrument panel crossmember, lower A-pillar, and floor harness) and inspect the protective sleeve for damage. Focus on areas contacting sharp metal edges. Repair damaged wires and reroute them to avoid moving parts.
  • 5
    Control module verification: If the wiring harness and airbag are normal, check the ACM power supply (constant +12V), ground (G201, etc.), and CAN communication. If necessary, replace and recode the airbag control module.
  • 6
    System reset and verification: After repair, reconnect all components and the battery. Use the diagnostic tool to clear the fault codes and execute 'system self-learning' or 'configuration reset'. Turn the ignition switch to ON and verify the airbag warning light turns off. Perform a simulated crash test to confirm normal system operation.
Real-World Cases
BYD DTC AI Analysis

Song Pro DM front passenger seat occupancy sensor fault (B1726-00)

✓
After starting the vehicle, the airbag warning light on the instrument panel stays on constantly with no other warning lights present. The fault code is B1726-00, and the 'airbag off' indicator displays abnormally regardless of whether the front passenger seat is occupied. The BYD VDS2000 diagnostic tool confirmed only current fault B1726-00. Removed the front passenger seat, inspected the OCS sensor wiring harness connector underneath, and found slight oxidation on the connector pins. Measured the sensor resistance and found it fluctuating between 2.3–2.8 kΩ (the normal reading should be stable around 2.5 kΩ). Ruled out the Airbag Control Module (ACM); determined the cause to be internal poor contact within the sensor. Replaced the genuine front passenger seat occupancy sensor assembly (Part No.: 6A-5823450). After replacement, performed the seat occupancy sensor calibration procedure: entered the SRS system → Special Functions → OCS Calibration with the diagnostic tool, followed the prompts to place a standard weight (75 kg dummy or equivalent sandbag) to complete the learning process. Cleared the fault codes and road-tested for 20 km without the light reappearing.
BYD DTC AI Analysis

Qin Plus EV airbag warning light stays on after accident repair

✓
After front-end accident repairs (seats undamaged in collision), airbag light stayed on. Read DTCs B1726-00 and U0151 (intermittent loss of communication with ACM). Checked airbag control module power and ground – normal; CAN bus voltage normal at ~2.5V. Inspected passenger seat wiring harness carefully. Found the 4-pin OCS sensor connector under the seat not fully latched from the previous seat removal/refitting, causing an intermittent connection. Wiggling the harness changed DTC status between 'current' and 'history', confirming the poor contact. Inspected seat rail mounting bolts; found one bolt too long, pressing against the wiring harness sheath and causing an intermittent open circuit in the internal wires. Repaired the connector contacts, applied conductive grease, plugged in firmly, and secured harness routing with cable ties. Replaced seat mounting bolts with correct length (previous repair shop used wrong specification). Used Launch X431 to perform 'collision data clear' and 'system configuration reset'. Fault resolved. No recurrence at one-week follow-up.
BYD DTC AI Analysis

Tang DM-i front passenger seat sensor signal drift fault

✓
Passenger seat airbag indicator normally turns off when an adult sits. When a child (about 30 kg) or a heavy object is placed on the seat, the indicator acts erratically, sometimes showing ‘airbag on’ and sometimes ‘off’, eventually triggering DTC B1726-00. Connected a dedicated diagnostic tool and read the OCS real-time data stream. The sensor output voltage jumped erratically between 0.8 V and 3.2 V (normally it should rise steadily with increasing weight). Removed the seat foam and found the OCS sensor mat (pressure sensing mat) partially folded, causing uneven load distribution. Traced the cause: the owner had previously fitted full-coverage seat covers; pulling during removal displaced the sensor mat. Removed the seat upholstery, re-laid the OCS sensor pressure mat flat, ensuring no creases. Checked the adhesion points between the sensor mat and seat foam, and re-fixed the edges with double-sided tape. Used no replacement parts; recalibrated after reassembly. Calibration method: performed ‘zero-point calibration’ with no load, then placed a 75 kg weight and performed ‘full-load calibration’.
BYD DTC AI Analysis

High-mileage BYD e5 wiring harness chafed and shorted

✓
At 280,000 km, the airbag warning light started illuminating intermittently. DTC B1726-00 was stored as a history code, occurring every few days and correlating with road roughness. The front passenger seat was frequently occupied, so the sensor saw heavy use. Initial inspection found no external harness damage; the connectors were secure. We used an oscilloscope to measure the OCS sensor signal waveform and found that the signal line had momentary shorts to ground when driving on rough surfaces. After stripping back the harness protective sheath for a detailed inspection, we discovered the wiring beneath the seat had rubbed against the metal edge of the seat rail during repeated height adjustments, wearing through the insulation and causing intermittent shorts. Tests also detected sensor aging, with static resistance drifting by more than 10%. We repaired the damaged harness: cut out the worn section, re-soldered the connections, and insulated them with heat-shrink tubing. We re-routed the harness away from the seat rail travel path and added corrugated tubing for protection. Given the high mileage and sensor aging, we also replaced the OCS sensor assembly (aftermarket approx. ¥280, OEM ¥650; this repair used the OEM part). The calibration procedure completely eliminated the fault.
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.