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 — Seal U

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 Seal U indicates an open circuit in the left curtain shield 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 or poorly connected yellow airbag connector near the B- or C-pillar, or broken/worn wiring in the roof-side harness. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left curtain airbag connector loose or poor contact: The dedicated yellow connector above the B-pillar or C-pillar is not fully locked, or pinching after interior trim panel repair caused terminal back-out.
  • 2Wiring harness broken or worn: Repeated long-term bending at the door hinge breaks the internal copper strands of the wiring harness between the A-pillar and roof side rail, or the edge of the routing hole wears through the insulation, causing an open circuit.
  • 3Airbag module internal fault: Abnormal resistance or open circuit in the curtain airbag inflator squib due to aging, moisture ingress, or manufacturing defects.
  • 4SRS ECU terminal oxidation: Water ingress or a damp environment oxidized the terminals connecting the floor wiring harness to the SRS control unit, 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 improperly mated the connector, 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: Use BYD VDS or a dedicated diagnostic tool to read fault codes, 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. Check if the curtain airbag wiring harness connector (yellow marking) fully seats and locks. Check if the connector locating pin is broken.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector (located under the centre console or centre tunnel). Use a digital multimeter to measure the resistance between the pins of the left curtain airbag circuit. Normal value: 2.0-3.0 Ω. If the multimeter displays OL (open circuit), continue troubleshooting 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. Individual 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 re-run 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, securely 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 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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.