AU
B1708

DTC B1708 indicates the airbag control unit (SRS ECU) detects a 0-ohm resistance in the left side curtain airbag ignition circuit — Atto 8

Safety System

DTC B1708 indicates the airbag control unit (SRS ECU) detects a 0-ohm resistance in the left side curtain airbag ignition circuit.

This typically indicates a short circuit in the ignition circuit (short to ground or short between positive and negative terminals).

Under normal operating conditions, the airbag igniter resistance must measure between 2.0 and 3.0 ohms to generate sufficient Joule heat to trigger the gas generator during a collision.

A 0-ohm reading means the circuit has virtually no resistance.

Potential causes include an internal short circuit in the curtain airbag igniter, wiring harness damage causing direct contact between positive and negative terminals, connector water ingress and corrosion, or a fault in the SRS ECU internal detection circuit.

This fault prevents the left side curtain airbag from deploying normally during a side impact (current bypasses the igniter) or, in extreme cases, creates a risk of unintended deployment.

This critical fault severely compromises passive safety functions.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Internal short circuit in the left side curtain airbag igniter: Damaged insulation on the ignition bridge wire inside the gas generator or moisture in the propellant shorts the internal positive and negative terminals. Measured resistance is close to 0Ω.
  • 2Harness wear short circuit: Vehicle vibration, collision crushing, or sharp sheet metal edges damage the insulation on the harness from the SRS ECU to the left curtain airbag (usually routed along the A-pillar, B-pillar, and C-pillar), causing direct contact between the positive and negative wires.
  • 3Connector water ingress or corrosion: Poor sealing of the dedicated yellow airbag connector located below the A-pillar, inside the B-pillar trim panel, or at the door sill causes internal pins to short circuit after water exposure, or long-term oxidation causes an abnormal decrease in resistance.
  • 4Internal SRS ECU fault: Damage to the firing circuit monitoring chip, sampling resistor, or A/D conversion circuit inside the airbag control unit causes a false 0 resistance reading, while the actual curtain airbag and wiring harness are normal.
  • 5Improper repair procedures: Plugging or unplugging the airbag connector during accident repairs without disconnecting the battery as specified, causing electrostatic breakdown; or failing to fully lock the connector, allowing a terminal pin to back out and contact the metal body, creating a short to ground.
What To Do
  • 1
    Safety Preparation and Diagnostic Confirmation: Use the VDS2000/VDS3100 diagnostic tool to read and confirm fault code B1708. Record the freeze frame data (vehicle speed, temperature, etc. at the time of occurrence). Disconnect the negative battery terminal and wait at least 3 minutes to fully discharge the SRS backup power supply capacitor.
  • 2
    Visual and connector inspection: Remove the left A-pillar, B-pillar, and C-pillar trim panels. Inspect the left curtain airbag module for visible damage. Thoroughly inspect the yellow dedicated connector (usually located at the bottom of the A-pillar or middle of the B-pillar) for looseness, water ingress, bent pins, or green corrosion.
  • 3
    Isolate and locate the fault: Use a dedicated airbag tester (or a digital multimeter with current-limiting protection) to measure: ① Curtain airbag terminal resistance (disconnect the connector and measure the curtain airbag side; normal resistance is 2-3Ω; if 0Ω, replace the curtain airbag); ② Wiring harness terminal resistance (measure the harness from the ECU to the connector for a short to ground or power; resistance must be infinite).
  • 4
    Harness continuity and insulation test: Measure harness continuity between the SRS ECU connector and the left curtain airbag connector (must be less than 1 Ω). Use a megohmmeter to measure harness-to-body insulation resistance (must be greater than 1 MΩ). Specifically check for wear at the rubber grommets where the harness passes through the firewall and door sill.
  • 5
    Replacement verification and repair: If the curtain airbag resistance measures 0 Ω, replace the left-side curtain airbag assembly (Note: check the new part's production date; do not use expired airbags). If the wiring harness has a short circuit, repair the wiring harness and reroute it to avoid contact with sharp edges. If the curtain airbag and wiring harness are normal, replace the SRS ECU.
  • 6
    System reset and matching: Connect the battery and clear the fault code. If replacing the SRS ECU or curtain airbag, use the diagnostic tool to perform 'Airbag System Configuration Write' (write the vehicle VIN and airbag configuration code). Perform a Key-On self-check. Confirm B1708 does not return and the instrument cluster airbag warning lamp turns off.
Real-World Cases
BYD DTC AI Analysis

2021 BYD Tang left curtain airbag internal short circuit

✓
While driving normally, the dashboard suddenly displayed 'Check Airbag System'. A VDS scan showed only B1708 (left curtain airbag resistance 0 Ω). I removed the left C-pillar trim and disconnected the yellow connector on the curtain airbag. Using a dedicated tester, I measured 0.3 Ω at the curtain terminal (standard: 2.5 Ω ± 0.5 Ω) and confirmed an internal short in the igniter bridge wire. I replaced the left curtain airbag assembly (Part No.: ...), then cleared the fault codes and reconfigured the SRS system with a diagnostic tool, which fixed the problem. Root cause: moisture in the igniter propellant from a specific gas generator production batch caused an internal micro-short.
BYD DTC AI Analysis

2019 BYD Yuan EV airbag warning light on after wading through water.

✓
After driving through water about 40 cm deep, the airbag warning light on the instrument panel stayed on. VDS scan showed DTCs B1708 and B1706 (left side curtain airbag short to ground). Removed the left sill trim panel and found the airbag harness connector under the left front sill. The waterproof seal had perished and detached, and water had clearly entered. A water film between the pins caused a short circuit (measured 0.1 Ω). Cleaned the connector with anhydrous alcohol, dried it with compressed air, applied special conductive anti-corrosion grease, and replaced the seal. Curtain airbag resistance returned to normal (2.4 Ω). Cleared fault codes, system normal.
BYD DTC AI Analysis

2019 BYD Song MAX: False DTCs after accident repair

✓
After repairing a left-side collision, the dashboard kept showing an airbag fault. VDS retrieved DTC B1708. Inspection found that while reinstalling the left curtain airbag, the technician inserted the yellow connector but did not hear the secondary lock (CPA) click, leaving the connector not fully seated. The ECU detected abnormal loop resistance (contact resistance near 0Ω). The connector was reseated and the lock tab fully engaged (two clicks heard). The DTC was cleared using VDS, and the SRS system self-test (including an ignition cycle) was completed, eliminating the fault. This is a typical false electrical fault caused by human error.
BYD DTC AI Analysis

2020 BYD Qin petrol — wiring harness chafing caused short circuit

✓
After 3 years and 80,000 km, the vehicle logged a B1708 fault. Lifted the vehicle and inspected the chassis harness. Found the left curtain airbag harness chafed through at the A-pillar lower sheet metal hole, where prolonged vibration against the sharp edge wore through the protective sleeve and insulation. The internal positive and negative wires were exposed and made direct contact, causing a short circuit (resistance: 0Ω). Cut out the damaged harness section (approx. 15 cm), rejoined with waterproof soldering, and insulated with double-layer heat shrink tubing. Rerouted the harness, added a rubber protective sleeve, and secured with cable ties to prevent body contact. Fault fully cleared.
Other Atto 8 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.