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 6 EV

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 6 EV indicates a high-severity short to ground in the ignition circuit for the left second-row seat belt pretensioner. This can disable the pretensioner and affect SRS operation. Common causes include damaged or pinched under-seat/B-pillar wiring, or water/corrosion in the yellow pretensioner connector. Do not probe or repair SRS wiring yourself; visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
4
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Frequent fore-and-aft seat adjustment or pinching damages the wiring harness insulation under the seat or inside the B-pillar trim panel, causing the wire to contact the vehicle body metal frame and short to ground.
  • 2After vehicle wading, heavy rain, or deep interior cleaning, water enters the pretensioner connector (yellow plug, usually located under the seat), causing terminal-to-terminal or terminal-to-ground short circuits and corrosion.
  • 3Manufacturing defect or aging of the pyrotechnic squib inside the seat belt pretensioner causes the resistance wire to short to the metal housing.
  • 4Internal drive circuit or monitoring circuit fault in the airbag control unit (SRS ECU) causes a false detection and reports 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 rails or metal brackets.
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the negative battery terminal, and wait at least 90 seconds for the SRS capacitor to fully discharge, preventing accidental pretensioner deployment and personal injury during inspection and repair.
  • 2
    Visual inspection: Remove the left middle-row seat (or move the seat to the fully forward or rearmost position). Locate the seat belt pretensioner connector (usually a yellow waterproof plug). Inspect for damage, water stains, burn marks, or recessed pins.
  • 3
    Wiring check: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the harness side (Vehicle Side) signal pin and body ground. The normal reading is infinity (OL). If the multimeter 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 check: Measure the resistance between the two pins on the pretensioner side (Component Side). The normal value is 1.5-3.0 Ω. If the resistance is 0 Ω or very low (<1 Ω), this indicates an internal short circuit in the pretensioner. Replace the seat belt assembly (the pretensioner is usually unavailable 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 restore battery power. Use a VDS or X431 diagnostic tool to clear the fault code and perform an SRS system self-check. Verify DTC B177C11 does not return and the airbag warning light turns off.
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 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.