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 — Seal 6 EV

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 Seal 6 EV indicates low resistance in the left side curtain airbag squib circuit, usually meaning a short circuit. Severity is medium because it can disable airbag protection or affect deployment. Common causes include moisture or aging inside the 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.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Internal moisture ingress or aging in the left curtain airbag gas generator (igniter) short circuits the internal resistance wire, dropping the resistance below 1.0 Ω.
  • 2Long-term vibration, compression, or wear of the wiring harness in the roof side rail or B-pillar trim damages the insulation of the positive and negative wires, causing a short circuit between wires or a short to ground.
  • 3Water ingress at the wiring harness connector near the left A-pillar, B-pillar, or C-pillar (usually a yellow waterproof plug) caused by vehicle wading, a leaking blocked sunroof drain, or improper car washing, resulting in an electrolytic short circuit between terminals.
  • 4Faulty SRS ECU (airbag control module) internal detection circuit 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 disconnecting and reconnecting the airbag connector without disconnecting the battery) cause igniter damage or circuit faults.
What To Do
  • 1
    Safety preparation: Power 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, left B-pillar upper trim, and the left edge of the headliner. Visually inspect the left curtain airbag wiring harness and connector (yellow marking) for obvious damage, burn marks, water ingress, or terminal back-out.
  • 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) to check for short circuits.
  • 4
    Igniter resistance measurement: Remove the left curtain airbag assembly (avoid rough handling). Directly measure the resistance between the igniter terminals using a dedicated airbag tester or a multimeter (ensure no-current-output mode). The normal value is 1.5Ω-3.0Ω. A reading below 1.0Ω indicates a faulty curtain airbag.
  • 5
    Simulator verification: Connect a 2.0Ω dedicated airbag simulator (substitute resistor) to the original curtain airbag harness. Connect the battery, turn the ignition ON, and read the fault codes 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 persists, check the SRS ECU or harness.
  • 6
    Fault repair: Replace the left curtain airbag assembly (when replacing, use genuine parts and record the explosive component 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 confirm B1709-00 does not reappear; perform a road test or simulated vibration test and 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 Seal 6 EV 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.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.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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.