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 — Qin Plus

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 Qin Plus indicates low resistance in the left side curtain airbag squib circuit, usually meaning a short circuit. This is a medium-severity SRS fault because it can disable the airbag or affect deployment in a crash. Common causes include moisture or aging inside the airbag inflator, or damaged wiring in the roof rail or B-pillar. 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
  • 1Moisture ingress or aging inside the left-side curtain airbag inflator (igniter) causes a short circuit in the internal resistance wire, reducing resistance below 1.0 Ω.
  • 2Long-term vibration, compression, 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 ingress in the wiring harness connector near the left A-pillar, B-pillar, or C-pillar (usually a yellow waterproof plug) due to vehicle wading, leakage from a blocked sunroof drain, or improper car washing causes an electrolytic short circuit between the terminals.
  • 4SRS ECU (airbag control module) internal detection circuit fault or damaged sampling resistor, causing a false low resistance reading for the left curtain airbag.
  • 5Improper repair procedures (such as using a standard multimeter resistance setting to directly measure the airbag igniter circuit, or connecting and disconnecting the airbag connector without disconnecting the battery) damage the igniter or cause a circuit fault.
What To Do
  • 1
    Safety preparation: Turn off the vehicle, disconnect the negative battery cable, and wait at least 90 seconds (ensuring the SRS backup power supply discharges completely) to prevent accidental airbag deployment during inspection.
  • 2
    Initial inspection: Remove the left A-pillar trim, left B-pillar upper trim, and left edge of the headliner. Visually inspect the left curtain airbag wiring harness and connector (yellow mark) for obvious damage, burn marks, water ingress, or backed-out terminals.
  • 3
    Harness continuity check: Disconnect the wiring harness between the SRS ECU and the left curtain airbag. Use a digital multimeter to measure the resistance between the curtain airbag-side harness terminal and body ground (should be greater than 1 MΩ) and the resistance between the harness terminals (should be open circuit or infinite) to check for a short circuit.
  • 4
    Igniter resistance measurement: Remove the left curtain airbag assembly (avoid rough handling). Directly use a dedicated airbag tester or a multimeter (set to no-current-output mode) to measure the resistance between the igniter terminals. The normal value is 1.5 Ω - 3.0 Ω. If the measured value is below 1.0 Ω, 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 read the fault code using the diagnostic tool. 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 (when replacing, use genuine parts and record the explosive device traceability information), repair the wiring harness short circuit or service the water-ingressed connector, and replace the SRS ECU if necessary.
  • 7
    System reset and verification: Clear all fault codes, perform an SRS system self-diagnosis (KOEO test), and verify B1709-00 does not return. Perform a road test or simulated vibration test to verify 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 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.