AU
B1705

DTC B1705 indicates the airbag control module (SRS ECU) detects a short to ground in the left curtain shield airbag ignition circuit — Seal U

Safety System

DTC B1705 indicates the airbag control module (SRS ECU) detects a short to ground in the left curtain shield airbag ignition circuit.

During self-diagnostics or real-time monitoring, the ECU detects the insulation resistance between the left curtain airbag ignition line (typically designated as pins FL- or F5) and body ground falls below the threshold (typically <2Ω).

This indicates a short-to-ground path in the ignition circuit, which may cause: 1) Curtain airbag fails to deploy during a collision (current shorts to ground and cannot ignite the gas generator). 2) Risk of unintended curtain airbag deployment under abnormal conditions (intermittent poor contact at the short point generates sparks).

This constitutes a hard fault in the active safety system.

The ECU immediately illuminates the SRS warning light and disables the entire airbag system (including driver, passenger, and side airbags), eliminating side-impact protection.

The B1705 fault code on the Seal U indicates a short to ground in the left curtain airbag ignition circuit. This is a high-severity SRS fault that can disable the airbag system and prevent proper curtain airbag deployment. Common causes include damaged wiring along the A/B-pillar or roof rail, or water ingress and corrosion at connectors. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Physical damage to the wiring harness: The left curtain airbag wiring harness (usually routed along the A-pillar, B-pillar, and roof side rail) rubs against sharp metal body edges, damaging the insulation and causing the copper core to contact the frame directly. Common after vehicle wading, interior trim removal and installation, or accident repairs.
  • 2Connector water ingress and corrosion: A poorly sealed airbag wiring harness connector inside the left front door sill trim or below the B-pillar allows water entry during car washing, wading, or high-humidity conditions. This causes a short circuit between pins or between pins and the housing (ground), forming an oxide layer that results in abnormal resistance to ground.
  • 3Internal gas generator fault: Insulation failure of the igniter (squib) inside the left curtain airbag assembly short-circuits the ignition pins to the curtain airbag metal bracket or vehicle body. Airbag aging, previous impact damage, or manufacturing defects usually cause this.
  • 4SRS ECU internal monitoring circuit fault: A damaged voltage monitoring chip or sampling resistor inside the airbag control module generates a false short-to-ground report. Related fault codes for other airbag circuits usually accompany this condition, or the fault occurs intermittently.
  • 5Ground interference or incorrect wiring: During installation of a dash cam, ambient lighting, or aftermarket audio system, installers mistakenly use the curtain airbag wiring harness as a ground wire, or bundle the curtain airbag wiring harness too tightly with the ground wire during routing, causing insulation damage.
What To Do
  • 1
    Safety preparation: Move the vehicle to a well-ventilated area, turn off the ignition switch, disconnect the 12V battery negative terminal, and wait at least 90 seconds (to ensure the SRS ECU energy storage capacitor fully discharges, preventing accidental airbag deployment and personal injury).
  • 2
    Initial visual inspection: Remove the left A-pillar trim, B-pillar trim, and left roof trim. Carefully inspect the wiring harness along the left curtain airbag harness routing (from the SRS ECU to the left C-pillar). Check contact points with the metal frame, harness retaining clips, and pass-through holes for insulation damage, burn marks, or crushing.
  • 3
    Electrical isolation test: Disconnect the SRS ECU connector (located under the centre console or inside the centre armrest) and the left curtain airbag connector (usually located at the C-pillar or roof side rail). Use a multimeter to measure the resistance between the curtain airbag-side wiring harness and body earth. Normal resistance is infinite (OL). A continuity reading (<1Ω) confirms the wiring harness is shorted to earth.
  • 4
    Section-by-section localization: If diagnostics confirm a short circuit, use the section-by-section isolation method to troubleshoot. Measure the curtain airbag body resistance at the curtain airbag connector (normal: 2.0-3.0Ω). If normal, the short circuit is in the wiring harness. Check the intermediate connectors (such as the B-pillar mating connector) and inspect each section sequentially to locate the short circuit.
  • 5
    Repair or replace: For damaged wiring harnesses, repair the insulation using heat-shrink tubing or waterproof tape, and reroute the harness to avoid contact with sharp edges. For corroded connectors, clean the terminals, apply conductive grease, and replace the connector if necessary. If the curtain airbag itself has a short circuit, replace the complete left-side curtain airbag assembly (non-repairable).
  • 6
    System verification: After repair, reconnect all connectors and the battery. Use a VDS or X431 diagnostic tool to clear the fault code and perform an SRS system self-check (Active Test). Verify B1705 does not return and the SRS warning light turns off. Finally, perform a road test to confirm the fault does not recur under vehicle vibration.
Real-World Cases
BYD DTC AI Analysis

Left curtain airbag connector corroded and short-circuited after water ingress.

✓
A 2020 BYD Song MAX came in with the SRS warning light on after driving through deep water during heavy rain. Diagnostics pulled fault code B1705. Removing the left front sill trim exposed the airbag harness connector beneath the B-pillar, which contained a significant amount of muddy water. Green corrosion was present between pin 3 (curtain airbag negative) and the metal connector shell, with a measured resistance of 0.8 ohms. The cause was traced to aged door seals that allowed water to enter through the B-pillar when wading. Repair involved cleaning the connector thoroughly, drying the harness with compressed air, fitting a waterproof replacement connector, and resealing the area. The fault cleared.
BYD DTC AI Analysis

Wiring harness pinched after accident repair, causing intermittent short circuit

✓
After a left-side collision repair, the SRS warning lamp illuminated intermittently on a 2019 BYD Yuan EV. The diagnostic scan tool showed historic fault code B1705. Inspection revealed that when the left rear quarter panel was replaced, the technician had not clipped the curtain airbag wiring harness into its retaining channel correctly. The harness was trapped between the C-pillar trim clip and the bodywork, causing intermittent shorts to ground during vibration. Solution: Rerouted the harness, repaired damaged insulation, and secured the harness using genuine clips to maintain adequate clearance from the body. The fault has not recurred.
BYD DTC AI Analysis

A-pillar modification caused the curtain airbag circuit to short to ground

✓
A 2021 BYD Tang triggered a B1705 fault immediately on startup after installing A-pillar tweeters. Inspection found the modification shop had incorrectly connected the speaker ground wire to the curtain airbag harness shield, and poor insulation caused it to contact the chassis. Since the curtain airbag ignition circuit has extremely low resistance to ground (normally it should be floating), the ECU judged this as a short circuit. Solution: remove the improper wiring, restore the factory harness, reroute the speaker wiring to a proper body ground point, and clear the fault codes. The system returned to normal.
BYD DTC AI Analysis

Igniter insulation failure inside the curtain airbag assembly

✓
2019 BYD Qin petrol, no accident or modification history. At 80,000 km, the SRS warning light illuminated intermittently, and DTC B1705 would not clear. Wiring harness measurements showed normal continuity from the ECU to the curtain airbag connector, but the resistance between the left curtain airbag igniter pin and the airbag's metal bracket was 0.3Ω (should be infinite). Diagnosed as an internal short in the inflator. Replaced the left curtain airbag assembly (part number must match vehicle VIN) and performed system configuration and coding. Fault resolved.
BYD DTC AI Analysis

SRS ECU software false positive (false fault)

✓
A 2021 BYD Tang displayed an SRS warning on the instrument cluster after an infotainment system upgrade. The scan retrieved DTC B1705 along with several unrelated airbag codes. The left curtain airbag harness resistance was normal at 2.3 Ω, with good insulation to ground. The problem was traced to 12V power fluctuations during the upgrade, which corrupted data in the SRS ECU. Performed an SRS ECU initialisation/reset using VDS, refreshed calibration data, and cleared the codes. The fault did not return—a confirmed software false alarm.
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.