AU
B1784-00

This fault code indicates a low resistance or short circuit in the driver-side front airbag Stage 2 inflator circuit — Atto 3

Safety System

This fault code indicates a low resistance or short circuit in the driver-side front airbag Stage 2 inflator circuit.

The SRS control unit detects a circuit resistance of 0 ohms (normal range: 2.0-3.0 ohms).

Dual-stage airbag systems deploy based on collision severity: Stage 1 provides partial inflation, and Stage 2 provides full deployment for maximum protection.

A 0-ohm resistance typically indicates a short circuit in the inflator itself, the internal wiring of the clock spring (spiral cable), or a wiring harness short to ground.

This fault causes the SRS system to identify a risk of unintended Stage 2 deployment.

Consequently, the system illuminates the airbag warning light and may disable the entire driver-side front airbag, severely compromising occupant protection during a collision.

The B1784-00 fault code on the Atto 3 indicates a medium-severity short circuit or very low resistance in the driver-side front airbag Stage 2 inflator circuit. Common causes include a shorted steering wheel clock spring or a fault inside the driver airbag’s second-stage igniter. The airbag warning light may come on and protection may be reduced. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Internal winding of the steering wheel clock spring (spiral cable) short-circuits or breaks and shorts to ground. This is a common steering system failure point on the BYD Qin series.
  • 2Short circuit in driver airbag assembly internal second-stage igniter (airbag assembly fault, possibly due to aging or manufacturing defect)
  • 3Long-term steering wear damages the airbag wiring harness insulation near the steering column, causing a short circuit to the steering wheel metal frame.
  • 4Internal drive circuit fault in the SRS control unit (ACU) causing a false code (confirm after ruling out wiring faults)
  • 5Water ingress into the airbag connector (especially the grey connector below the steering wheel) after vehicle wading or interior deep cleaning causes a short circuit between terminals.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds for the SRS backup power supply to discharge completely to prevent accidental airbag deployment.
  • 2
    Initial inspection: Remove the service covers on both sides of the steering wheel, disconnect the airbag module connector, and check the connector terminals for green oxidation, water stains, or deformation.
  • 3
    Measure the airbag module: Use a digital multimeter to measure the resistance between the Stage 2 squib pins on the airbag module side. Normal resistance is 2.0-3.0 Ω. If the resistance is close to 0 Ω, replace the driver airbag assembly.
  • 4
    Inspect the clock spring: Disconnect the wiring harness connector below the clock spring and measure the resistance to ground on the lower side (towards the SRS ECU). If the resistance is not infinite, inspect the wiring harness. Measure continuity between the corresponding upper and lower terminals of the clock spring. If abnormal, replace the clock spring assembly.
  • 5
    Wiring harness inspection: Carefully inspect the yellow SRS wiring harness sleeve between the steering column and the steering wheel for wear or crush marks. Specifically check for a pinched harness at the steering column tube retaining clip.
  • 6
    System reset: After repair, reconnect all connectors (listen for the locking click). Connect the battery. Use the VDS2000 or Launch diagnostic tool to clear the fault codes. Perform the 'SRS system self-check' and 'igniter circuit test'.
  • 7
    Function check: Perform a simulated crash test (use the diagnostic tool to execute an actuator activation test without deployment). Confirm B1784-00 does not recur and all steering wheel functions (horn, multifunction buttons) operate normally.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV450 clock spring internal short circuit causing B1784-00

✓
2018 Qin EV450, 62,000 km. Airbag warning light on. DTCs B1784-00 and B1783-00 (first-stage resistance abnormal). Disassembly found the clock spring damaged during a previous steering wheel modification. Measuring continuity from top to bottom showed 0.3Ω between second-stage circuit pins (normal: continuity with measurable resistance). Replaced with OEM clock spring (part number: BYD-3658310-XX). Second-stage circuit resistance restored to 2.4Ω. Cleared codes; system normal.
BYD DTC AI Analysis

Qin 100 airbag connector corroded and short-circuited after water wading

✓
2017 BYD Qin 100. After driving through water, instrument cluster displayed "Check SRS System". Scanning revealed active DTC B1784-00. Removed driver airbag; connector (grey 2-pin) had significant water staining and green corrosion. Cleaned and dried terminals, but still measured 0Ω — igniter internally short-circuited. Replaced driver airbag module (new mounting bolts required) and applied anti-corrosion treatment to wiring harness connector. Fault resolved.
BYD DTC AI Analysis

Aftermarket steering wheel caused wiring harness to chafe and short circuit.

✓
A 2017 BYD Qin 80 showed an airbag warning light after the owner installed a third-party steering wheel cover and modifications. Diagnostics revealed intermittent DTC B1784-00. Inspection found the SRS wiring harness had not been secured correctly during the modification; it was rubbing against a metal bracket inside the steering column, wearing through the insulation and causing an intermittent short to ground. Repaired the damaged wiring with high-temperature tape and corrugated tubing, then re-routed and secured the harness to factory specifications with adequate slack for steering wheel rotation. The fault did not recur.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.