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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.

3
Cases Logged
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.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.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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.