AU
B1704-00

DTC B1704-00 indicates the SRS (Supplemental Restraint System) ECU detects an open circuit fault in the left curtain shield airbag ignition circuit — Atto 3

Safety System

DTC B1704-00 indicates the SRS (Supplemental Restraint System) ECU detects an open circuit fault in the left curtain shield airbag ignition circuit.

The SRS ECU continuously monitors the airbag inflator circuit resistance via an internal diagnostic circuit.

When the resistance value exceeds the normal threshold (typically >10Ω or approaching infinity), the ECU registers a 'disconnected' state.

This fault prevents the left curtain airbag from deploying during a side impact, depriving the occupant's head of lateral impact protection and posing a severe safety hazard.

Interrupted electrical connections, damaged wiring harnesses, or a failed inflator within the airbag module can cause this fault.

The B1704-00 fault code on the Atto 3 indicates an open circuit in the left curtain airbag ignition circuit. This is a medium-severity SRS fault because the airbag may not deploy in a side impact. Common causes include a loose yellow airbag connector near the pillar or damaged roof-side wiring. The recommended fix is inspection and repair by an authorised dealer. Typical repair cost data is available from recorded cases.
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Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Left curtain airbag connector loose or poor contact: dedicated yellow connector above the B-pillar or C-pillar not fully locked, or pinched after interior trim repairs, causing terminal back-out.
  • 2Broken or worn wiring harness: Long-term repeated bending at the door hinge breaks the internal copper strands of the wiring harness between the A-pillar and the roof side rail, or the edge of the routing hole wears through the insulation, causing an open circuit.
  • 3Internal airbag module fault: Aging, moisture ingress, or manufacturing defects cause abnormal resistance or an open circuit in the curtain airbag inflator igniter tube (Squib).
  • 4SRS ECU terminal oxidation: Terminals connecting the floor wiring harness to the SRS control unit oxidize due to water ingress or damp environments, increasing contact resistance.
  • 5Safety shorting clip not reset: During collision repairs, the technician failed to remove the shorting clip from the airbag connector or mate the connector correctly, causing the shorting clip to bypass the circuit.
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the 12V battery negative cable, and wait at least 90 seconds to fully discharge the SRS backup power capacitor and prevent accidental airbag deployment.
  • 2
    Fault Confirmation: Read the fault code using BYD VDS or a dedicated diagnostic tool. Confirm B1704-00 is a current fault (Active). Record freeze frame data (crash sensor status, vehicle speed, etc.).
  • 3
    Visual inspection: Remove the left A-pillar, B-pillar, and C-pillar trim panels. Check if the curtain airbag wiring harness connector (yellow mark) is fully inserted and locked. Inspect the connector locating pin for breakage.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector (located under the centre console or centre tunnel). Measure the resistance between the left curtain airbag circuit pins using a digital multimeter. Standard value: 2.0-3.0 Ω. If the reading is OL (open circuit), continue inspecting the wiring harness.
  • 5
    Harness continuity test: Measure harness continuity from the SRS ECU to the airbag module. Inspect for breaks at the harness retaining clips near the B-pillar and inside the door hinge corrugated conduit. Individual wire resistance must be <1 Ω.
  • 6
    Simulated load test: Connect a dedicated 2Ω SRS simulation resistor to the wiring harness end in place of the airbag module. Clear the fault code and rerun the self-check. If the fault code disappears, the airbag module is faulty. Replace the left curtain airbag assembly.
  • 7
    Repair verification: After repairing the wiring harness or replacing the component, fully seat all connectors (listen for the locking 'click'), reconnect the battery, clear the fault code, and perform an SRS system self-check. Confirm the fault code does not reappear and the airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Left B-pillar connector not reconnected after accident repair, causing intermittent warnings

✓
A 2018 Qin EV450 developed an intermittent airbag warning light after left front door sheet metal repair. VDS scan showed DTC B1704-00 (current). Removed the left B-pillar trim and found the curtain airbag connector (yellow) only partially inserted—about halfway—with the locking tab not engaged. The technician had removed interior trim during the repair and did not properly reseat the connector; the connector requires two audible clicks to confirm full engagement. Re-seated the connector fully and wrapped it with electrical tape for added security. Cleared the DTC; no recurrence.
BYD DTC AI Analysis

Blocked sunroof drain tube caused wiring harness corrosion and open circuit

✓
A 2019 BYD E1 developed a constant airbag warning light after heavy rain, logging DTC B1704-00. Inspection found water staining below the left A-pillar. Removing the headliner revealed the left curtain airbag harness connector covered in green copper corrosion; the severely oxidised pins caused contact resistance >50 Ω. Further inspection showed the left rear sunroof drain hose had detached, allowing rainwater to track down the A-pillar. Replaced the left curtain airbag harness assembly (including connector), cleaned the SRS ECU terminals, re-secured the drain hose, and resolved the fault.
BYD DTC AI Analysis

Aftermarket roof lining modification accidentally severed airbag harness.

✓
A 2017 BYD Qin 80 came in with an illuminated airbag warning light after a starlight headliner retrofit. The scan tool displayed DTC B1704-00. Disassembly revealed that the retrofit technician had accidentally drilled through the protective corrugated tubing of the curtain airbag wiring harness while drilling into the left roof rail, severing two wires. The curtain airbag wiring harness is a non-serviceable part integrated into the roof harness and cannot be repaired separately. The shop replaced the entire left roof wiring harness (including the curtain airbag branch) and coded and matched the SRS ECU to resolve the fault.
BYD DTC AI Analysis

Curtain airbag module internal squib open circuit due to aging

✓
The airbag warning light suddenly illuminated on a 2017 Qin EV300 with 120,000 km, logging DTC B1704-00. Resistance at the harness end measured 2.3 Ω (normal), but a direct measurement at the airbag module terminals showed open circuit (OL). Removed the left curtain airbag (after removing the front and rear sections of the headliner) and found a cold solder joint on the igniter pin inside the gas generator, causing the open circuit. Replaced the left curtain airbag module with a genuine part, performed the 'Replace Airbag Module' configuration procedure using a diagnostic tool, and fixed the fault. This is a rare but possible hardware failure mode in high-mileage vehicles.
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.