AU
B1708

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

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.

The B1708 fault code on the Seal U indicates a short circuit in the left side curtain airbag ignition circuit, with the SRS ECU detecting 0-ohm resistance instead of the normal 2.0–3.0 ohms. Severity is medium because it can stop the curtain airbag deploying correctly and may affect safety. Common causes include a shorted curtain airbag igniter or damaged wiring along the pillars. 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 U
  • 1Left curtain airbag igniter internal short circuit: Damaged igniter bridge wire insulation inside the gas generator or moisture in the propellant shorts the internal positive and negative terminals. Resistance measures close to 0Ω.
  • 2Harness chafing short circuit: Vehicle vibration, accident compression, or sharp sheet metal edges damage the insulation on the harness between the SRS ECU and the left curtain airbag (typically routed along the A, B, and C-pillars), causing direct contact between the positive and negative wires.
  • 3Connector water ingress or corrosion: The yellow airbag-specific connector located below the A-pillar, inside the B-pillar trim panel, or at the door sill is poorly sealed, causing internal pins to short circuit after driving through water, or allowing long-term oxidation to cause an abnormal drop in resistance.
  • 4Internal SRS ECU fault: A damaged ignition circuit monitoring chip, sampling resistor, or A/D conversion circuit inside the airbag control unit causes a false resistance reading of 0, while the actual curtain airbag and wiring harness are normal.
  • 5Improper repair operations: Plugging or unplugging the airbag connector without disconnecting the battery as specified during accident repairs, causing electrostatic breakdown; or failing to fully lock the connector, allowing a terminal 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 battery negative 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 the middle of the B-pillar) for looseness, water ingress, bent pins, or copper corrosion.
  • 3
    Fault isolation: 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 2-3 Ω; if 0 Ω, replace the curtain airbag); ② wiring harness terminal resistance (check 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 1Ω). Use a megohmmeter to measure harness-to-body insulation resistance (must be greater than 1MΩ). Inspect the rubber grommets for wear where the harness passes through the firewall and door sills.
  • 5
    Replacement, verification, and repair: If the curtain airbag resistance is 0 Ω, replace the left curtain airbag assembly (Note: Check the production date of the new part; do not use expired airbags). If the wiring harness has a short circuit, repair and reroute the harness 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 codes. 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 DTC 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 Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.