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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 — Qin Plus

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 Qin Plus indicates an open circuit in the left curtain airbag ignition circuit. This is a medium-severity SRS fault because the left curtain airbag may not deploy in a side impact. Common causes include a loose B-pillar or C-pillar airbag connector, poor pin contact, or a broken/worn roof-side wiring harness. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Left curtain airbag connector loose or poor contact: Yellow dedicated connector above the B-pillar or C-pillar is not fully locked, or compression during interior trim panel repairs caused pin 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, causing an open circuit.
  • 3Internal airbag module fault: Curtain airbag inflator igniter (squib) exhibits abnormal resistance or open circuit due to aging, moisture ingress, or manufacturing defects.
  • 4SRS ECU terminal oxidation: Terminals connecting the floor wiring harness to the SRS control unit oxidize due to water ingress or a damp environment, increasing contact resistance.
  • 5Safety shorting clip not reset: During accident vehicle repairs, the technician failed to remove the shorting clip from the airbag connector or properly mate the connector, 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 to fully discharge the SRS backup power supply capacitor and 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) and 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. Inspect 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 left curtain airbag circuit pins. The normal value is 2.0-3.0 Ω. If the reading shows OL (open circuit), continue troubleshooting the wiring harness.
  • 5
    Harness continuity test: Measure harness continuity from the SRS ECU to the airbag module. Check specifically for breaks at the harness retaining clips near the B-pillar and inside the door hinge corrugated tube. Single wire resistance must be <1Ω.
  • 6
    Simulated load test: Connect a dedicated 2Ω SRS simulation resistor to the wiring harness connector in place of the airbag module. Clear the fault code and perform a 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, mate all connectors correctly (listen for a locking "click"). Reconnect the battery, clear the fault code, perform an SRS system self-check, and 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 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.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.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.