AU
B1784

DTC B1784 indicates the driver-side front airbag Stage 2 firing circuit resistance is 0 ohms, signifying a short to ground or an internal short circuit in the gas generator secondary firing circuit — Seal U

Safety System

DTC B1784 indicates the driver-side front airbag Stage 2 firing circuit resistance is 0 ohms, signifying a short to ground or an internal short circuit in the gas generator secondary firing circuit.

Modern airbag systems use a staged deployment strategy: Stage 1 deploys during moderate collisions, while Stage 2 deploys during severe collisions based on parameters such as seat position and seat belt usage to enhance protection.

A resistance of 0 ohms means the SRS ECU detects circuit impedance below the threshold (typically less than 1.0Ω).

This triggers the safety lockout mechanism and disables the airbag.

This fault severely compromises driver protection during a collision and requires immediate repair.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal wire breakage and short to ground or an interlayer short circuit in the airbag clock spring (spiral cable/clockspring) causes the stage 2 ignition circuit to short to ground.
  • 2Internal short circuit in the driver airbag module secondary squib, or inflator body fault (manufacturing defect or long-term moisture causing internal short circuit).
  • 3Airbag wiring harness connector (usually located under the steering wheel or near the main crossmember): water ingress, terminal back-out, or damaged insulation causing a short to body ground.
  • 4Improper repair procedures (such as removing the airbag without disconnecting the negative battery terminal) causing accidental deployment or wiring damage resulting in a short circuit.
  • 5Internal fault in the SRS control unit detection circuit (such as a burnt sampling resistor or damaged A/D converter) causes a false 0-ohm reading.
What To Do
  • 1
    Safe power down: Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect VDS or a dedicated diagnostic tool to read DTCs. Confirm B1784 is a current fault code (Active) and cannot be cleared. Record freeze frame data.
  • 3
    Visual inspection: Check the clock spring connector below the steering wheel and the airbag wiring harness corrugated tube for damage, water ingress, or burn marks. Check for oxidized or backed-out pins.
  • 4
    Resistance measurement: Remove the driver airbag module using the special tool. Disconnect the connector. Measure the resistance from both stage 2 ignition circuit terminals to ground (expected: infinite). Measure the circuit resistance (normal: 2.0-3.0 Ω). 0 Ω confirms a short circuit.
  • 5
    Sectional isolation: Disconnect the clock spring from the wiring harness. Measure the resistance on the airbag side, clock spring side, and body wiring harness side separately to pinpoint whether the short circuit is in the airbag unit, clock spring, or main wiring harness.
  • 6
    Component replacement: Replace the faulty component based on the diagnostic results (replace the clock spring first, then check the wiring harness, and finally consider the airbag module). Never use a multimeter to directly measure the airbag igniter.
  • 7
    System reset: Reconnect all connectors (ensure locking tabs are fully engaged), turn on the power, use the diagnostic tool to clear the fault code, and perform 'Collision Output Check' and 'Configuration Information Write'.
  • 8
    Function verification: Run the SRS system self-diagnosis and confirm B1784 does not return. Read the data stream to verify the stage 2 airbag resistance is within the normal range (2.0±0.5Ω). Perform a road test to confirm.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM driver airbag second stage circuit short to ground (B1784)

✓
Symptom: Instrument panel airbag warning light stayed on. VDS scan showed B1784 (driver second stage front airbag resistance 0 Ω). Diagnosis: With the battery disconnected, inspection found pin 3 of the clock spring connector G10 under the steering wheel had backed out and touched the metal bracket, shorting the second stage squib circuit to ground. Airbag module measured 2.3 Ω (normal); harness side read 0 Ω to ground. Resolution: Re-seated the backed-out pin, re-routed and secured the harness to clear the steering column, and installed a protective sleeve to prevent chafing. Cleared the fault code; resistance returned to 2.1 Ω and the warning light went out.
Original source ↗
BYD DTC AI Analysis

BYD Han EV airbag system intermittently sets B1784

✓
Symptoms: When driving over speed bumps or rough roads, the instrument cluster intermittently displayed 'Check Airbag System', with fault code B1784. Diagnostic process: Found the fault consistently reproduced at a specific steering wheel angle (left turn approximately 15°). Disassembly revealed the clock spring's internal ribbon cable rubbing against the housing at full lock, wearing through the insulation and causing intermittent shorts to ground. Resistance measured normal at rest, but dropped to 0Ω when turning the steering wheel. Solution: Replaced the clock spring assembly, re-centered the installation, and calibrated the steering angle sensor to the SRS system.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro reports B1784 fault with zero resistance after repair

✓
Symptoms: After the dealership replaced the steering column, the vehicle immediately threw a B1784 on startup. Secondary airbag resistance read 0Ω. Diagnosis: The technician skipped standard procedure. During steering wheel installation, the steering column mounting bolt crushed the airbag harness, grounding the secondary igniter line directly to the chassis. Disassembly revealed torn harness insulation with copper wires contacting the frame. Fix: Replaced the entire airbag harness, rerouted the wiring to maintain clearance from metal edges, and reinforced protection with insulation tape. Post-repair insulation resistance measured >10MΩ. Fault cleared.
Original source ↗
Other Seal U 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.