AU
B176F11

DTC B176F11 indicates the airbag control unit (SRS ECU) detects an abnormally low-resistance connection between the left rear seat belt pretensioner (squib) circuit and body ground (typically <2Ω) — Seal U

Safety System

DTC B176F11 indicates the airbag control unit (SRS ECU) detects an abnormally low-resistance connection between the left rear seat belt pretensioner (squib) circuit and body ground (typically <2Ω).

The pretensioner is a pyrotechnic actuator with a normal resistance of approximately 2.0-3.0Ω.

A short to ground causes the SRS system to identify a safety risk in this circuit and trigger fail-safe mode.

This mode immediately cuts power to the pretensioner circuit, illuminates the airbag warning lamp, and disables left rear pretensioner deployment during a collision.

It may also affect the normal deployment logic of the entire airbag system.

This is a hard DTC.

The SRS ECU continuously logs the code while the short circuit exists.

Repair the fault immediately to maintain passive safety system integrity.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Chafed wiring harness under left rear seat: Fore-and-aft seat adjustment or pinching by objects damages the pretensioner wiring harness insulation, causing a short circuit to the vehicle body metal frame.
  • 2B-pillar wiring harness interference: The wiring harness retaining clip inside the left rear B-pillar trim panel detached, causing the harness to rub against a sharp sheet metal edge and short to ground.
  • 3Connector water ingress and corrosion: Rear floor water exposure or interior cleaning allows water to enter the pretensioner connector (usually located under the seat or at the base of the B-pillar), causing electrolytic corrosion between the pins and resulting in a short to ground.
  • 4Pretensioner body internal fault: Insulation failure of the pretensioner internal squib shorts the pyrotechnic chamber to the housing, causing an internal short to ground.
  • 5Improper repair procedures: Fixing screws pierce or pinch the wiring harness when installing seat covers, modifying seat heating, or removing and installing interior trim, causing a hidden short circuit.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Read freeze frame: Use the VDS2000/VDS3000 diagnostic tool to read environmental data (temperature, vehicle speed, voltage) at the time of the fault to confirm if it is an intermittent fault.
  • 3
    Visual inspection: Remove the left rear seat. Inspect the pretensioner wiring harness (yellow sleeve) beneath the seat frame for abrasion, crushing, or damage. Inspect the connector at the bottom of the B-pillar for water ingress or green corrosion.
  • 4
    Resistance measurement: Disconnect the SRS ECU and pretensioner connectors. Use a multimeter to measure the resistance to ground on the pretensioner-side wiring harness. The normal value is ∞ (infinity). A reading of <10Ω confirms a short to ground.
  • 5
    Sectional inspection: If the wiring harness appears normal, use the sectional isolation method. Gradually strip back the harness sleeve from the pretensioner end toward the ECU end to locate the short circuit point. Focus inspection on the seat slide rail fixing bolts and the protective rubber grommets where the harness passes through sheet metal holes.
  • 6
    Component test: If the wiring harness is normal, directly measure the pretensioner body resistance. Standard value: 2.0 ± 0.3 Ω. If the resistance is <1 Ω or has continuity to ground, replace the left rear seat belt pretensioner assembly.
  • 7
    Repair verification: After repairing the wiring harness (apply double-layer insulation wrapping with heat-shrink tubing) or replacing the component, reconnect all connectors. Clear the fault code. Perform the SRS system self-diagnosis and verify it passes. Finally, perform a full-range seat adjustment test to confirm no interference.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM left rear seat rail wear caused pretensioner short circuit

✓
Vehicle at 30,000 km with the airbag warning light constantly illuminated. VDS scan showed DTC B176F11. Disassembly found the pretensioner wiring harness (yellow) pinched by the bolt washer at the rear mounting point of the left rear seat rail. Long-term seat adjustment wore through the harness insulation, exposing the copper core to the seat frame (ground). Fix: Loosened the seat rail mounting bolts, pulled out the damaged harness, wrapped it with high-temperature tape and enclosed it in corrugated tubing, rerouted the harness clear of the rail travel range, then retightened the bolts and installed a rubber protective grommet. Cleared the DTC; SRS system returned to normal.
BYD DTC AI Analysis

E2 EV B-pillar water ingress caused pretensioner connector corrosion and short circuit.

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Southern region vehicle. Airbag warning light came on after heavy downpour; DTC B176F11. Found damp carpet at base of left rear B-pillar. Removed B-pillar trim and found pretensioner connector (2-pin yellow plug) had water staining and green copper corrosion. Measured resistance between pin 1 (ground) and pin 2 (pretensioner circuit) at only 0.8Ω. Cause: Perished sunroof drain hose joint at upper B-pillar allowed water to track down trim into lower connector. Repair: Replaced sunroof drain hose joint. Cleaned connector pins with electrical contact cleaner, dried with compressed air, and applied conductive paste. Confirmed insulation resistance to ground >10MΩ. Reassembled and cleared fault.
BYD DTC AI Analysis

False pretensioner short-circuit warning after seat cover replacement on Qin EV

✓
Customer reported the airbag warning light came on while driving after installing leather seat covers at an external auto trim shop. VDS detected DTC B176F11. Inspection revealed the installer used long self-tapping screws penetrating the seat foam to secure the covers; screw tips pierced the yellow sleeve of the pretensioner harness, shorting to ground. Repair: Removed improperly installed screws. Found wiring damage with 2 locations of exposed conductors. Cut out damaged section, soldered connections, and applied double-layer heat-shrink tubing. Relocated mounting points to avoid harness routing. Advised owner to avoid SRS wiring paths during modifications.
BYD DTC AI Analysis

BYD Qin Pro Fuel Pretensioner Body Internal Short Circuit Replacement Case

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The vehicle had no accident history, but intermittently set DTC B176F11—sometimes returning hours after clearing. Visual check of the wiring harness showed no damage. Pretensioner body resistance measured 0.3Ω with continuity to ground, indicating the internal squib igniter insulation had broken down. Removed the left rear seatbelt pretensioner (requires seat assembly removal), installed a new assembly (part number possibly 4C-XXXXXX), and torqued the mounting bolts to 7-9 N·m. Reconnected and the fault cleared permanently. Returned part analysis confirmed an internal manufacturing defect caused premature failure.
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.