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 8

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 8 indicates an open circuit in the left curtain shield airbag ignition circuit. Severity is medium, but it can stop the left curtain airbag from deploying in a side impact. Common causes include a loose yellow airbag connector near the B- or C-pillar, or damaged wiring in the roof/door area. Visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 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 panel repairs, causing terminal back-out.
  • 2Wiring harness broken or worn: Long-term repeated bending at the door hinge breaks the internal copper wires in the harness between the A-pillar and the roof side rail, or the edge of the wiring hole wears through the insulation layer, causing an open circuit.
  • 3Internal airbag module fault: Aging, moisture ingress, or manufacturing defects cause abnormal resistance or an open circuit in the igniter (squib) inside the curtain airbag inflator.
  • 4SRS ECU terminal oxidation: Water ingress or a damp environment oxidizes the terminals connecting the floor wiring harness to the SRS control unit, increasing contact resistance.
  • 5Safety shorting clip not reset: During collision repairs, the technician did not remove the shorting clip from the airbag connector or mate the connector properly, causing the shorting clip to bypass the circuit.
What To Do
  • 1
    Safety preparation: Turn off the ignition, disconnect the 12V battery negative cable, and wait at least 90 seconds for the SRS backup power capacitor to fully discharge to prevent accidental airbag deployment.
  • 2
    Fault Confirmation: Use BYD VDS or a dedicated diagnostic tool to read the fault code. 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. Verify the curtain airbag wiring harness connector (yellow marking) fully seats and locks. Check the connector locating pin for breakage.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector (located under the center console or center tunnel). Use a digital multimeter to measure the resistance between the pins of the left curtain airbag circuit. The normal value is 2.0-3.0 Ω. If the multimeter displays OL (open circuit), continue inspecting the wiring harness.
  • 5
    Harness continuity test: Measure harness continuity from the SRS ECU end to the airbag module end. Inspect specifically for breaks at the harness retaining clips near the B-pillar and inside the door hinge corrugated conduit. Single wire resistance must be <1Ω.
  • 6
    Simulated load test: Connect a dedicated 2Ω SRS simulation resistor to the wiring harness 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 components, correctly mate all connectors (listen for a locking 'click'). Reconnect the battery, clear the fault code, and perform an SRS system self-check. Confirm the fault code does not return 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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.