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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 — Qin Plus

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 Qin Plus indicates a high-severity short to body ground in the left second-row seat belt pretensioner ignition circuit. This can disable the pretensioner and affect SRS operation. Common causes include damaged under-seat or B-pillar wiring from seat movement, or water/corrosion in the yellow pretensioner connector. Do not probe the circuit yourself; visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Frequent fore-and-aft seat adjustment or pinching wears through the wiring harness insulation under the seat or inside the B-pillar trim panel, causing the exposed 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 (typically the yellow plug under the seat), causing a short circuit or corrosion between terminals or from a terminal to ground.
  • 3Manufacturing defect or aging of the pyrotechnic squib inside the seat belt pretensioner assembly causes the resistance wire to short to the metal housing.
  • 4Fault in the airbag control unit (SRS ECU) internal drive or monitoring circuit causes a false detection and triggers 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 and prevent 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), and inspect it for damage, water stains, burn marks, or terminal back-out.
  • 3
    Wiring check: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the wiring harness side (Vehicle Side) signal pin and body ground. Normal resistance is infinite (OL). If the reading indicates continuity (0Ω or close to 0Ω), inspect along the wiring harness for chafing points. Focus on the seat slide rail, inside the B-pillar trim panel, and the floor wiring harness channel.
  • 4
    Component check: Measure resistance between the two pins on the pretensioner side (Component Side). The normal value is 1.5-3.0Ω. If resistance is 0Ω or extremely low (<1Ω), this indicates an internal short circuit in the pretensioner body. 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 battery. Use the VDS or X431 diagnostic tool to clear the fault code and perform an SRS system self-check. Confirm 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 Qin Plus 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.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 Qin Plus →Qin Plus 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.