AU
B1709-00

DTC B1709-00 indicates the resistance of the LH Side Curtain Airbag (also known as the head side airbag) squib circuit falls below the normal threshold set by the SRS ECU (typically below 1 — Atto 3

Safety System

DTC B1709-00 indicates the resistance of the LH Side Curtain Airbag (also known as the head side airbag) squib circuit falls below the normal threshold set by the SRS ECU (typically below 1.0Ω).

The standard airbag squib resistance normally ranges from 1.5Ω to 3.0Ω.

Low resistance essentially indicates a short circuit.

An internal squib short, a wiring harness short to ground, a short between connector terminals, or a faulty SRS ECU internal detection circuit can cause this condition.

This fault causes the airbag control unit to detect an abnormal circuit, illuminate the SRS warning lamp continuously, and potentially activate the system protection mechanism (disabling the LH side curtain airbag and related airbags).

In extreme cases, the short circuit can cause unintended airbag deployment in non-collision conditions (though unlikely due to the SRS ECU dual trigger logic).

Alternatively, current shunting can prevent proper airbag deployment during a side impact, severely compromising occupant head safety.

The B1709-00 fault code on the Atto 3 indicates low resistance in the left side curtain airbag squib circuit, usually meaning a short circuit. Severity is medium because the SRS warning light may stay on and the airbag may not work correctly. Common causes include a shorted airbag igniter or damaged wiring in the roof rail or B-pillar. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Moisture ingress or aging inside the left curtain airbag gas generator (igniter) shorts the internal resistance wire, reducing the resistance below 1.0 Ω.
  • 2Long-term vibration, pinching, or wear damages the insulation of the positive and negative wires in the roof side rail or B-pillar trim wiring harness, causing a short circuit between wires or a short to ground.
  • 3Water enters the wiring harness connector near the left A-pillar, B-pillar, or C-pillar (usually a yellow waterproof plug) due to vehicle wading, a blocked and leaking sunroof drain, or improper car washing, causing an electrolytic short circuit between terminals.
  • 4Internal fault in the SRS ECU (airbag control module) detection circuit or damaged sampling resistor, causing a false low resistance reading for the left curtain airbag.
  • 5Improper repair procedures (such as directly measuring the airbag igniter circuit with a standard multimeter in resistance mode, or connecting or disconnecting the airbag connector without disconnecting the battery) damage the igniter or cause circuit faults.
What To Do
  • 1
    Safety Preparation: Turn off the vehicle, disconnect the negative battery cable, and wait at least 90 seconds (to fully discharge the SRS backup power supply) to prevent accidental airbag deployment during inspection.
  • 2
    Initial inspection: Remove the left A-pillar trim, B-pillar upper trim, and the left edge of the headliner. Visually inspect the left curtain airbag wiring harness and connector (yellow identification) for obvious damage, burn marks, signs of water ingress, or backed-out terminals.
  • 3
    Harness continuity check: Disconnect the harness between the SRS ECU and the left curtain airbag. Use a digital multimeter to measure the resistance between the curtain airbag-side harness terminals and body ground (should be greater than 1 MΩ), and the resistance between the harness terminals (should be open circuit or infinite). Check for a short circuit.
  • 4
    Igniter resistance measurement: Remove the left curtain airbag assembly (avoid excessive force). Directly measure the resistance between the igniter terminals using a dedicated airbag tester or a multimeter (verify no-current-output mode). The standard value is 1.5Ω to 3.0Ω. If the measured value is below 1.0Ω, the curtain airbag itself is faulty.
  • 5
    Simulator verification: Connect a 2.0Ω dedicated airbag simulator (substitute resistor) to the original curtain airbag wiring harness. Connect the battery, turn the ignition ON, and use the diagnostic tool to read the fault code. If the fault code changes to a history code or disappears, the fault is in the curtain airbag assembly. If the fault remains, check the SRS ECU or wiring harness.
  • 6
    Fault repair: Replace the left curtain airbag assembly (if replacing, use genuine parts and record the explosive device traceability information), repair the wiring harness short circuit or water-ingressed connector, and replace the SRS ECU if necessary.
  • 7
    System reset and verification: Clear all fault codes and perform an SRS system self-diagnosis (KOEO test) to confirm B1709-00 does not return. Perform a road test or simulated vibration test to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV300: SRS warning light on after driving through water, left curtain airbag resistance too low

✓
The owner of a 2017 Qin EV300 reported the airbag warning light stayed on constantly after driving through floodwater during a heavy rain. We connected a VDS2000 diagnostic scanner and retrieved codes B1709-00 (Left curtain airbag resistance too low) and B170A-00 (Left curtain airbag short to ground). Upon disassembly and inspection, we found the left rear sunroof drain hose had detached, allowing water to run down the A-pillar and severely oxidise the inside of the yellow left curtain airbag wiring harness connector under the B-pillar, causing a short between the terminals. We replaced the wiring harness connector (including the seal and terminals), thoroughly dried the harness with compressed air, cleared the codes and fixed the fault. We advised the owner to regularly check the sunroof drain hoses to keep them clear.
BYD DTC AI Analysis

Qin 80 intermittently sets DTC B1709-00 after accident repair

✓
A 2017 BYD Qin 80 suffered a left-side impact. The dealership replaced the left side curtain airbag and left front door after the collision. The vehicle operated normally following the repair, but two weeks later the SRS warning light began illuminating intermittently. A scan tool displayed DTC B1709-00 (current fault). Inspection found that during the repair, screws securing the B-pillar trim panel had crushed the new curtain airbag harness, damaging the insulation and exposing the copper wires. On rough roads, the damaged section intermittently shorted against the vehicle body. The fix: re-route the harness away from sharp sheet metal edges, repair the wiring using insulating tape and corrugated tubing, and adjust the trim panel clip positions. This completely resolved the fault.
BYD DTC AI Analysis

BYD Qin EV450 left side curtain airbag inoperative after headliner refurbishment

✓
A 2018 Qin EV450 came in with the airbag warning light on after an Alcantara headliner retrim at an unauthorised modification shop. Diagnostics flagged DTC B1709-00 (left curtain airbag resistance too low). Investigation found that during headliner removal, the shop technicians had not disconnected the battery and used metal tools to pry open the curtain airbag connector, causing an internal short in the igniter (measured resistance only 0.3 Ω). Since the damage was permanent (resistance cannot recover), we replaced the left curtain airbag assembly with a new unit and coded and matched the SRS ECU. Airbag system repairs must be performed only by qualified technicians; working on live circuits is strictly prohibited.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.