AU
B177C11

DTC B177C11 indicates a short circuit to body ground (GND) in the ignition trigger circuit of the left middle-row (second-row left) seat belt pretensioner — Seal U

Safety System

DTC B177C11 indicates a short circuit to body ground (GND) in the ignition trigger circuit of the left middle-row (second-row left) seat belt pretensioner.

The pretensioner is a critical component of the SRS (Supplemental Restraint System).

It contains a pyrotechnic ignition device (squib).

During a collision, the airbag control unit (ACU) triggers the squib with a specific current to instantly tighten the seat belt and protect the occupant.

This DTC indicates the ACU detected abnormally low resistance in the pretensioner circuit (close to 0Ω), falling outside the normal threshold (typically 1.5–3.0Ω).

Potential causes include damaged wiring insulation contacting the vehicle frame, water ingress at the connector shorting the terminal to ground, or an internal short between the pretensioner resistance wire and the metal housing.

This critical safety fault disables the pretensioner for the affected seat and may trigger the SRS fail-safe mode, preventing proper airbag deployment.

Extreme cases pose a risk of unintended heat generation or ignition.

The B177C11 fault code on the Seal U indicates a high-severity short to ground in the ignition trigger circuit for the left second-row seat belt pretensioner. This can disable the pretensioner and may affect SRS operation. Common causes include damaged under-seat or B-pillar wiring insulation, or water entering the yellow pretensioner connector and causing corrosion or shorts. Visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Frequent fore-and-aft seat adjustment or crushing wears through the wiring harness insulation under the seat or inside the B-pillar trim panel, causing the wire to contact the metal body frame and create a short to ground.
  • 2After vehicle wading, heavy rain, or deep interior cleaning, water enters the pretensioner connector (usually a yellow plug under the seat), causing terminal-to-terminal or terminal-to-ground short circuits or corrosion.
  • 3Manufacturing defect or aging of the pyrotechnic squib inside the seat belt pretensioner body, causing the resistance wire to short circuit to the metal housing.
  • 4Internal drive circuit or monitoring circuit fault in the airbag control unit (SRS ECU) causes false detection and sets a short-to-ground fault code.
  • 5During seat modification, floor mat installation, or third-party repairs, overtightened screws or cable ties damage the wiring harness insulation, or improper harness routing causes dynamic interference with the seat slide rail or metal bracket.
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor. This prevents accidental pretensioner activation and personal injury during inspection and repair.
  • 2
    Visual inspection: Remove the left middle-row seat (or move the seat to the foremost/rearmost position), locate the seat belt pretensioner connector (usually a yellow waterproof plug), and inspect the connector for damage, water stains, burn marks, or backed-out pins.
  • 3
    Circuit inspection: Disconnect the pretensioner connector and use a multimeter to measure the resistance between the wiring harness side (Vehicle Side) signal pin and body ground. Normal resistance is infinity (OL). If the reading shows continuity (0Ω or close to 0Ω), inspect the wiring harness for chafing points, focusing on the seat slide rail, inside the B-pillar trim panel, and the floor wiring harness channel.
  • 4
    Component inspection: Measure the resistance between the two pins on the pretensioner side (Component Side). The normal value is 1.5-3.0Ω. If the resistance is 0Ω or extremely low (<1Ω), this indicates an internal short circuit in the pretensioner. Replace the seat belt assembly (pretensioners are usually not available separately).
  • 5
    Repair verification: After repairing the wiring harness (cut out the damaged section, re-solder, insulate with heat-shrink tubing, and adjust routing to prevent interference) or replacing the pretensioner, reconnect the connector and the battery. Use a VDS or X431 diagnostic tool to clear the fault code and perform an SRS system self-check. Confirm DTC B177C11 does not return and the airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

BYD E2 seat rail chafed through wiring harness causing short circuit

✓
A 2019 BYD E2 with 32,000 km showed a steady airbag warning light on the instrument panel. VDS scan retrieved DTC B177C11. Technicians removed the left rear seat and found the pretensioner wiring harness had chafed through at the left seat rail mounting bracket. Exposed copper wire contacted the metal frame, causing a short to ground. They cut away the damaged harness section, resoldered the joints, insulated with double-layer heat shrink tubing, and repositioned the harness retaining clips to clear the seat rail travel. Fault cleared.
BYD DTC AI Analysis

Qin EV pretensioner connector corroded after water ingress

✓
A 2019 Qin EV showed an airbag system warning on the dash at startup the day after driving through flooded roads in heavy rain. DTC B177C11. Found water and green corrosion inside the pretensioner connector under the left rear seat, causing a signal terminal short to ground. Cleaned the connector contacts with electronic cleaner, dried with compressed air, and applied conductive protectant. Measured normal pretensioner resistance, reconnected the wiring, cleared the fault code. Back to normal.
BYD DTC AI Analysis

Abnormal internal resistance in E3 model pretensioner

✓
A 2020 BYD E3 with no collision or water damage history had an intermittent DTC B177C11 that would not clear. Disconnected the pretensioner connector and measured the unit resistance: 0.3Ω cold (abnormally low). Tapping the seat belt retractor caused the resistance to fluctuate, confirming an internal igniter short. Replaced the left middle row seat belt assembly (including pretensioner) and ran SRS system configuration and calibration with a scan tool. Fault cleared permanently.
BYD DTC AI Analysis

Seat modification pinched wiring harness, causing short circuit

✓
A BYD E2 came in with the airbag warning light on after the owner fitted racing seats, code B177C11 stored. Mounting bolts crushed the seatbelt pretensioner harness during the modification, damaging the insulation and shorting it to ground. Repaired the harness, rerouted the wiring to maintain safe clearance from the seat frame. Fault resolved.
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.