AU
B1705

DTC B1705 indicates the airbag control module (SRS ECU) detects a short to ground in the left curtain shield airbag ignition circuit — Atto 3

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.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Physical wiring harness damage: 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 located inside the left front door sill trim panel or below the B-pillar allows water ingress during car washing, wading, or high-humidity conditions. This causes a short circuit between pins or between the pins and the housing (ground), forming an oxide layer that results in abnormal resistance to ground.
  • 3Internal gas generator fault: Igniter (squib) insulation failure inside the left curtain airbag assembly shorts the igniter 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 causes a false short-to-ground report. This condition typically occurs intermittently or alongside related fault codes for other airbag circuits.
  • 5Ground interference or incorrect wiring: During the installation of dash cams, ambient lighting, or audio modifications, installers mistakenly use the curtain airbag wiring harness as a ground wire, or tie the curtain airbag wiring harness too tightly to 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 fully discharge the SRS ECU energy storage capacitor, 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 left curtain airbag wiring harness along its routing (from the SRS ECU to the left C-pillar). Focus on contact points with the metal frame, harness retaining clips, and pass-through holes. Look for insulation damage, burn marks, or signs of crushing.
  • 3
    Electrical isolation test: Disconnect the SRS ECU connector (located under the center console or inside the center armrest box) 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 ground. Normal resistance is infinite (OL). A continuity reading (<1Ω) confirms the wiring harness is shorted to ground.
  • 4
    Section-by-section fault isolation: To trace a confirmed short circuit, use the section-by-section isolation method. Measure the curtain airbag resistance at the curtain airbag connector (normal value: 2.0-3.0 Ω). If normal, the short circuit is in the wiring harness. Check intermediate connectors (such as the B-pillar mating connector) and inspect each section sequentially to locate the short circuit.
  • 5
    Repair or replace: • Damaged wiring harness: Repair the insulation with heat-shrink tubing or waterproof tape, and reroute the harness to avoid contact with sharp edges. • Corroded connectors: Clean the pins and apply conductive grease. Replace the connector if necessary. • Short-circuited curtain airbag: Replace the entire left-side curtain airbag assembly (non-repairable).
  • 6
    System Verification: After repair, reconnect all connectors and the 12V battery. Use a VDS or X431 diagnostic tool to clear the fault code, then perform an SRS system self-check (Active Test). Verify DTC B1705 does not return and the SRS warning lamp turns off. Finally, perform a road test to verify the fault does not return 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.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.
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.