AU
B176A-00

This DTC indicates the airbag control unit (SRS ECU) detects a 0-ohm resistance in the left rear seatbelt pretensioner circuit, indicating a Short to Ground fault — Seal U

Safety System

This DTC indicates the airbag control unit (SRS ECU) detects a 0-ohm resistance in the left rear seatbelt pretensioner circuit, indicating a Short to Ground fault.

As a pyrotechnic actuator, the pretensioner normally has a resistance of 2.0Ω-3.0Ω (depending on the vehicle model, typically 2.2Ω±0.3Ω).

A 0-ohm resistance means current returns directly to ground without passing through the load.

The SRS system identifies the pretensioner circuit as faulty.

During a collision, the pretensioner may fail to activate and tighten the seatbelt, severely compromising occupant protection.

This is a hard fault.

Once confirmed, the system continuously illuminates the airbag warning light.

Disconnecting the power usually fails to clear this fault.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Pretensioner body internal short circuit: Moisture, aging, or manufacturing defects cause an internal short circuit between the two terminals of the seat belt pretensioner squib.
  • 2Physical damage to the wiring harness: The seat slide rail crushes or chafes the left rear floor wiring harness or under-seat wiring harness, damaging the wire insulation and causing contact with the vehicle body metal.
  • 3Connector water ingress and corrosion: Vehicle wading, improper interior cleaning, or poor sealing causes water to enter the pretensioner connector (usually located under the seat or lower B-pillar), creating a short-circuit path between the pins.
  • 4Airbag control unit internal fault: A damaged monitoring circuit or sampling resistor inside the SRS ECU triggers a false short circuit fault (uncommon, but requires inspection).
  • 5Improper repair operation: Directly measuring the pretensioner using the resistance setting of a standard multimeter. Excessive test current causes an internal short circuit in the pretensioner or melts and fuses the bridge wire.
What To Do
  • 1
    Safety preparation: Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental deployment.
  • 2
    Initial visual inspection: Check the pretensioner connectors (yellow markings) under the left rear seat and lower B-pillar for looseness, water ingress, corrosion, or obvious burn marks.
  • 3
    Harness inspection: Follow the harness routing and inspect the harness sleeve for wear, crushing, or deformation where it passes the seat slide rails and floor panel holes. Specifically check for wires pinched by the seat fixing bolts.
  • 4
    Segmented measurement: Disconnect the pretensioner connector. Use a high-impedance digital multimeter (test current <1mA) or a dedicated SRS tester to separately measure the resistance between the pretensioner body pins (normal: 2-3 Ω) and the resistance to ground on the harness side (should be infinite).
  • 5
    Fault isolation: If the pretensioner body resistance is 0 Ω, replace the left rear seat belt assembly (the pretensioner usually integrates into the seat belt retractor; do not replace it separately). If the wiring harness shows continuity to ground, repair or replace the damaged harness section.
  • 6
    System reset: After repair, reconnect all components and restore battery power. Use a genuine BYD diagnostic tool (BYD-ED400 or Launch X431) to clear fault codes and perform an SRS system self-check (some models require configuration coding).
  • 7
    Function verification: Start the vehicle and confirm the instrument cluster SRS warning light turns off. Read the data stream to confirm the left rear pretensioner resistance reads normal (2.0-3.0Ω). Perform a simulated crash test (if conditions permit) to verify circuit integrity.
Real-World Cases
BYD DTC AI Analysis

Seat track pinch caused wiring harness short circuit

✓
A 2017 Qin EV300 had the SRS warning light on constantly. DTC B176A-00 stored. Inspection found the left rear seat had been removed; the floor harness was routed off-spec and trapped under the seat slide rail. Long-term seat movement wore through the insulation, exposing copper and shorting to ground. Removing the seat revealed crush marks and chafed insulation on the harness. Repair: Cut out the damaged section, soldered the wires and insulated with heat-shrink tubing, then re-routed and secured the harness to spec with >20mm clearance from the seat rails. Fault resolved.
BYD DTC AI Analysis

Water ingress in the rear seat area caused connector corrosion and short circuit.

✓
2018 BYD Qin EV450. After driving in rain, the dashboard displayed an airbag fault. Scan tool retrieved DTC B176A-00. Found water and green corrosion inside the left rear seatbelt pretensioner connector (yellow plug) beneath the left rear seat. The owner confirmed the vehicle had been driven through water up to sill level. Water seeped through the floor into the connector, shorting the pretensioner circuit pins. Fix: Thoroughly cleaned the connector with electronic cleaner, blew it dry, and applied precision instrument grease to the pins. Measured pretensioner resistance at 2.1Ω (normal). Cleared the fault codes and the system returned to normal. Also inspected and cleared the drain holes to prevent further water ingress.
BYD DTC AI Analysis

Replace pretensioner assembly due to internal fault

✓
A 2017 BYD Qin 100 with no accident history suddenly illuminated the SRS warning light. Diagnosis revealed DTC B176A-00. Disconnecting the pretensioner connector, we measured 0.2Ω across the pretensioner (near short) against a normal ~2.3Ω. The harness side showed good insulation to ground. Diagnosed as internal pyrotechnic squib short. Replaced the left rear seatbelt assembly (includes pretensioner). Recorded the old part serial number—pretensioners are safety-critical components. Configured the SRS system with the new pretensioner parameters using a diagnostic tool, cleared the fault codes, and road-tested to verify.
BYD DTC AI Analysis

Airbag control module software fault causing false fault codes

✓
A 2017 BYD Qin 80 had an intermittent SRS warning light. Retrieved DTC B176A-00, but measured the pretensioner resistance at 2.2Ω (normal) and found no harness faults. Wiggling the harness wouldn't reproduce the fault, and the light returned several days after clearing the code. The BYD technical bulletin shows this production batch has an SRS ECU software bug that falsely detects pretensioner short circuits during specific temperature or voltage fluctuations. Fix: Updated the airbag control unit software to V2.3 or above. Fault hasn't returned since. Rule out hardware issues before investigating software faults like this.
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.