AU
B176712

This DTC indicates the Airbag Control Unit (ACU) detects a short to positive (+B) in the RH front side curtain airbag ignition circuit — Seal U

Safety System

This DTC indicates the Airbag Control Unit (ACU) detects a short to positive (+B) in the RH front side curtain airbag ignition circuit.

Under normal conditions, the airbag ignition circuit remains in a high-resistance state (infinite) or exhibits a specific resistance (typically >2Ω) only during circuit diagnostics.

When the ACU detects continuous battery voltage (12V) or a resistance near 0Ω on this circuit, it logs a short to power.

This hardwire short circuit causes the following: 1) Airbag fails to deploy during a collision (power supply clamps the circuit); 2) Unintended airbag deployment in extreme cases (if the ACU drive circuit and the shorted point form a complete circuit); 3) The ACU enters fail-safe mode, cuts power to this circuit, illuminates the SRS warning light, and degrades overall airbag system functionality.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Worn harness insulation: The right front curtain airbag harness routes along the A-pillar and roof side rail. Long-term vibration or aging door seals cause the harness to rub against body metal edges. Damaged insulation allows the harness to contact power wires (e.g., reading light or sunroof motor power supply wires).
  • 2Connector water ingress and oxidation: An aged sealing ring on the airbag connector (usually yellow) located under the headliner or A-pillar allows water from car washes or sunroof leaks to form an electrolytic bridge between the pins, short-circuiting the ignition pin to the power supply pin.
  • 3Airbag Control Unit (ACU) internal fault: ACU internal ignition drive transistor breakdown or filter capacitor short circuit causes a continuous high-level output on this channel.
  • 4Damage from non-professional modifications: Mounting screws piercing the airbag wiring harness during dash cam or headliner ambient lighting installation, or mistakenly connecting the airbag circuit as a ground or power wire.
  • 5Airbag module internal short circuit: The bridge wire inside the curtain airbag inflator igniter shorts to the housing, or moisture in the igniter powder causes an abnormal drop in resistance.
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the ACU backup power supply. Wear an anti-static wrist strap. Never use a multimeter resistance setting to directly measure the airbag inflator.
  • 2
    Visual inspection: Remove the right A-pillar trim, rear headliner section, and right rear C-pillar trim. Check the curtain airbag wiring harness (yellow corrugated conduit) for signs of abrasion, crushing, or puncture. Focus on the rubber grommets where the harness passes through openings.
  • 3
    Connector diagnosis: Disconnect the connector between the ACU and the right front curtain airbag. Set a multimeter to voltage mode and measure the airbag-side wiring harness voltage to ground. A 12V reading confirms the wiring harness is shorted to power. Measure the resistance between the ACU-side pins and power to confirm the ACU has no internal short circuit.
  • 4
    Sectional isolation: Use a short-circuit detector or sectional disconnection method to divide the wiring harness into three sections: ACU to A-pillar, A-pillar to C-pillar, and C-pillar to airbag. Measure the insulation resistance to the power supply section by section to locate the short circuit.
  • 5
    Component replacement verification: If the wiring harness is normal, connect a dedicated airbag simulator (2Ω) to the ACU in place of the curtain airbag. Clear the fault code and power on for self-check. If the fault code disappears, replace the airbag module; if it remains, replace the ACU.
  • 6
    Repair verification: After repairing the damaged wiring harness (insulate with double-layer heat shrink tubing; do not simply wrap with electrical tape) or replacing the faulty component, reconnect all connectors and restore power. Use the diagnostic tool to perform 'SRS system self-test' and 'crash sensor calibration'. Confirm B176712 does not return and the SRS light turns off.
Real-World Cases
BYD DTC AI Analysis

BYD E2: Worn A-pillar wiring harness causing intermittent short circuit

✓
2019 E2, 80,000 km. SRS light intermittent, DTC B176712 intermittent. Found airbag harness inside right front A-pillar trim rubbing against sheet metal burr, insulation worn through exposing copper. Contacted reading lamp power wire over bumps. Repaired harness with heat-shrink tubing, rerouted and secured wiring, added rubber protective sleeve. Fault resolved.
BYD DTC AI Analysis

BYD Qin EV sunroof leak caused connector short circuit

✓
2019 Qin EV. SRS warning light stayed on after heavy rain with DTC B176712. The sunroof drain tube had detached, allowing water into the right-side headliner. The curtain airbag connector above the C-pillar had oxidized pins; a water film was conducting between the power and airbag igniter pins. Cleaned the connector pins, applied conductive grease, reattached the drain tube and replaced the connector seal. Issue resolved.
BYD DTC AI Analysis

E3: Wiring harness incorrectly connected during dash cam installation

✓
2020 model E3. Owner fitted a dashcam themselves and, when tapping power, mistakenly identified the airbag circuit in the roof harness as the ACC feed, causing a short-to-power in the right front side curtain airbag circuit. Inspection found the airbag harness inside the A-pillar had been stripped and connected to a power tap. Restored the original harness and replaced the damaged airbag harness assembly (reliability insufficient if repaired). Fault cleared.
BYD DTC AI Analysis

ACU internal driver circuit fault

✓
2019 BYD Qin EV repeatedly triggered DTC B176712. Replaced the airbag and wiring harness; fault persisted. Monitored ACU output with a scope and found 12V present on this channel immediately at power-on. Determined the ACU internal ignition driver chip had shorted. Replaced the airbag control unit (located beneath the center console), performed coding and sensor calibration. Normal operation restored.
BYD DTC AI Analysis

Curtain airbag inflator internal short circuit

✓
BYD E2. Following flood damage, DTC B176712 set. Removed the right front side curtain airbag and measured 0.3Ω between the gas generator ignition terminals (normal >2Ω). Internal moisture caused a short. Replaced the curtain airbag module (requires headliner removal) and inspected the other airbag modules on the same side. Confirmed no water ingress before reassembly. Fault resolved.
Other Seal U 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.